155 results on '"Martin Eckstein"'
Search Results
2. Theory of photoinduced ultrafast switching to a spin-orbital ordered hidden phase
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Jiajun Li, Hugo U. R. Strand, Philipp Werner, and Martin Eckstein
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Science - Abstract
Ultrafast excitation of materials can cause the formation of hidden phases that are not accessible in thermal equilibrium. Li et al. identify and investigate theoretically a hidden phase that can be accessed in systems with intertwined spin and orbital-ordering such as KCuF3.
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- 2018
- Full Text
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3. Quantum to classical crossover of Floquet engineering in correlated quantum systems
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Michael A. Sentef, Jiajun Li, Fabian Künzel, and Martin Eckstein
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Physics ,QC1-999 - Abstract
Light-matter coupling involving classical and quantum light offers a wide range of possibilities to tune the electronic properties of correlated quantum materials. Two paradigmatic results are the dynamical localization of electrons and the ultrafast control of spin dynamics, which have been discussed within classical Floquet engineering and in the deep quantum regime where vacuum fluctuations modify the properties of materials. Here we discuss how these two extreme limits are interpolated by a cavity which is driven to the excited states. In particular, this is achieved by formulating a Schrieffer-Wolff transformation for the cavity-coupled system, which is mathematically analogous to its Floquet counterpart. Some of the extraordinary results of Floquet engineering, such as the sign reversal of the exchange interaction or electronic tunneling, which are not obtained by coupling to a dark cavity, can already be realized with a single-photon state (no coherent states are needed). The analytic results are verified and extended with numerical simulations on a two-site Hubbard model coupled to a driven cavity mode. Our results generalize the well-established Floquet engineering of correlated electrons to the regime of quantum light. This opens up a pathway of controlling properties of quantum materials with high tunability and low energy dissipation.
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- 2020
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4. Effective doublon and hole temperatures in the photo-doped dynamic Hubbard model
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Philipp Werner and Martin Eckstein
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Crystallography ,QD901-999 - Abstract
Hirsch's dynamic Hubbard model describes the effect of orbital expansion with occupancy by coupling the doublon operator to an auxiliary boson. In the Mott insulating phase, empty sites (holes) and doubly occupied orbitals (doublons) become charge carriers on top of the half-filled background. We use the nonequilibrium dynamical mean field method to study the properties of photo-doped doublons and holes in this model in the strongly correlated regime. In particular, we discuss how photodoping leads to doublon and hole populations with different effective temperatures, and we analyze the relaxation behavior as a function of the boson coupling and boson energy. In the polaronic regime, the nontrivial energy exchange between doublons, holes, and bosons can result in a negative temperature distribution for the holes.
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- 2016
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5. Nonthermal Melting of Néel Order in the Hubbard Model
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Karsten Balzer, F. Alexander Wolf, Ian P. McCulloch, Philipp Werner, and Martin Eckstein
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Physics ,QC1-999 - Abstract
We study the unitary time evolution of antiferromagnetic order in the Hubbard model after a quench starting from the perfect Néel state. In this setup, which is well suited for experiments with cold atoms, one can distinguish fundamentally different pathways for melting of long-range order at weak and strong interaction. In the Mott insulating regime, melting of long-range order occurs due to the ultrafast transfer of energy from charge excitations to the spin background, while local magnetic moments and their exchange coupling persist during the process. The latter can be demonstrated by a local spin-precession experiment. At weak interaction, local moments decay along with the long-range order. The dynamics is governed by residual quasiparticles, which are reflected in oscillations of the off-diagonal components of the momentum distribution. Such oscillations provide an alternative route to study the prethermalization phenomenon and its influence on the dynamics away from the integrable (noninteracting) limit. The Hubbard model is solved within nonequilibrium dynamical mean-field theory, using the density-matrix renormalization group as an impurity solver.
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- 2015
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6. Nonequilibrium Dynamical Mean-Field Theory for Bosonic Lattice Models
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Hugo U. R. Strand, Martin Eckstein, and Philipp Werner
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Physics ,QC1-999 - Abstract
We develop the nonequilibrium extension of bosonic dynamical mean-field theory and a Nambu real-time strong-coupling perturbative impurity solver. In contrast to Gutzwiller mean-field theory and strong-coupling perturbative approaches, nonequilibrium bosonic dynamical mean-field theory captures not only dynamical transitions but also damping and thermalization effects at finite temperature. We apply the formalism to quenches in the Bose-Hubbard model, starting from both the normal and the Bose-condensed phases. Depending on the parameter regime, one observes qualitatively different dynamical properties, such as rapid thermalization, trapping in metastable superfluid or normal states, as well as long-lived or strongly damped amplitude oscillations. We summarize our results in nonequilibrium “phase diagrams” that map out the different dynamical regimes.
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- 2015
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7. First trimester abortion protocols by facility type in Switzerland and potential barriers to accessing the service
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Samuel Martin Eckstein, Stefanie von Felten, Laura Perotto, Romana Brun, and Denise Vorburger
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Medicine ,Science - Abstract
Abstract Simplified first-trimester abortion protocols are well established. However, data on the use of medical or surgical abortion protocols across Switzerland is lacking. We report protocol characteristics in abortion care for two different facility types, hospital vs private practices (office-based) in Switzerland. Furthermore, we investigate an association between protocol characteristics and the likelihood of following through with the abortion at the same facility. We also report abortion outcomes of an office-based cohort where doctors use simplified abortion protocols. This study consists of two parts. (i) Between April and July, 2019, we collected data regarding medical and surgical abortion protocols of institutions offering abortions, in a nationwide survey. We assessed whether the proportion of patients who followed through with the abortion (primary outcome) after first appointment was associated with predefined protocol characteristics, considered to complicate access to abortion services, using generalised estimating equations. (ii) We analysed abortion outcomes of six selected office-based facilities from January, 2008, to December, 2018, using simplified abortion protocols in accordance with the Worlds Health Organisation (WHO) guidelines. (i) We included a total of 39 institutions. Hospitals showed more protocol-based barriers to abortion access compared with office-based facilities. The odds of undergoing an abortion after the first appointment were increased using protocols with minimal barriers. Overall, office-based facilities applied higher gestational age limits, required fewer appointments, and administered mifepristone more often after the first visit than did hospitals. (ii) We included a total of 5274 patients with an incidence of complications requiring surgery of 2.5% in line with rates reported in published literature. Only a few hospitals provide abortion care with easy access to medical and surgical abortion, whereas most office-based facilities do. Access to abortion services is generally crucial, and should be provided in a single visit whenever clinically permissible.
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- 2023
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8. NESSi: The Non-Equilibrium Systems Simulation package.
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Michael Schüler, Denis Golez, Yuta Murakami, Nikolaj Bittner, Andreas Hermann 0005, Hugo U. R. Strand, Philipp Werner, and Martin Eckstein
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- 2019
9. NESSi: The Non-Equilibrium Systems Simulation package.
- Author
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Michael Schüler, Denis Golez, Yuta Murakami, Nikolaj Bittner, Andreas Hermann 0005, Hugo U. R. Strand, Philipp Werner, and Martin Eckstein
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- 2020
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10. MiR-205-driven downregulation of cholesterol biosynthesis through SQLE-inhibition identifies therapeutic vulnerability in aggressive prostate cancer
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Johannes Linxweiler, Mathias T. Rosenfeldt, Martin Eckstein, Burkhard Kneitz, Sven Wach, Kerstin Junker, Markus Krebs, F. Röhrig, M. Puhr, Martin Eilers, T. Frank, Hubert Kübler, H. Marouf, Matthias Saar, Charis Kalogirou, Anna Katharina Seitz, Werner Schmitz, P. Schmucker, Martin Spahn, E. Hartmann, Gabriele Büchel, Marteinn Thor Snaebjornsson, Andreas Müller, and Almut Schulze
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Male ,Squalene monooxygenase ,Antifungal drug ,General Physics and Astronomy ,Mice, SCID ,urologic and male genital diseases ,Cohort Studies ,Mice ,Prostate cancer ,chemistry.chemical_compound ,Transactivation ,Neoplasm Metastasis ,Cancer ,Aged, 80 and over ,Multidisciplinary ,Middle Aged ,Lipids ,Gene Expression Regulation, Neoplastic ,Prostatic Neoplasms, Castration-Resistant ,Cholesterol ,Receptors, Androgen ,lipids (amino acids, peptides, and proteins) ,Transcriptional Activation ,Cell death ,Cell Survival ,Science ,Down-Regulation ,Urological cancer ,General Biochemistry, Genetics and Molecular Biology ,Article ,Downregulation and upregulation ,Cell Line, Tumor ,medicine ,Animals ,Humans ,Enzalutamide ,Metabolomics ,Computer Simulation ,Neoplasm Invasiveness ,Terbinafine ,Aged ,Cell Proliferation ,Neoplasm Staging ,Base Sequence ,business.industry ,Prostatic Neoplasms ,General Chemistry ,Prostate-Specific Antigen ,medicine.disease ,Androgen receptor ,Disease Models, Animal ,MicroRNAs ,Squalene Monooxygenase ,chemistry ,Drug Resistance, Neoplasm ,Cancer research ,business - Abstract
Prostate cancer (PCa) shows strong dependence on the androgen receptor (AR) pathway. Here, we show that squalene epoxidase (SQLE), an enzyme of the cholesterol biosynthesis pathway, is overexpressed in advanced PCa and its expression correlates with poor survival. SQLE expression is controlled by micro-RNA 205 (miR-205), which is significantly downregulated in advanced PCa. Restoration of miR-205 expression or competitive inhibition of SQLE led to inhibition of de novo cholesterol biosynthesis. Furthermore, SQLE was essential for proliferation of AR-positive PCa cell lines, including abiraterone or enzalutamide resistant derivatives, and blocked transactivation of the AR pathway. Inhibition of SQLE with the FDA approved antifungal drug terbinafine also efficiently blocked orthotopic tumour growth in mice. Finally, terbinafine reduced levels of prostate specific antigen (PSA) in three out of four late-stage PCa patients. These results highlight SQLE as a therapeutic target for the treatment of advanced PCa., Cholesterol metabolism is involved in the progression of aggressive prostate cancer (PCa). Here the authors show that miR-205 downregulation promotes cholesterol synthesis and androgen receptor signalling in PCa through enhancing the expression of the rate-limiting enzyme of cholesterol synthesis, squalene epoxidase.
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- 2021
11. Dynamical mean-field study of a photon-mediated ferroelectric phase transition
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Katharina Lenk, Jiajun Li, Philipp Werner, and Martin Eckstein
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Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences - Abstract
The interplay of light and matter gives rise to intriguing cooperative effects in quantum many-body systems. This is even true in thermal equilibrium, where the electromagnetic field can hybridize with collective modes of matter, and virtual photons can induce interactions in the solid. Here, we show how these light-mediated interactions can be treated using the dynamical mean-field theory formalism. We consider a minimal model of a two-dimensional material that couples to a surface plasmon polariton mode of a metal-dielectric interface. Within the mean-field approximation, the system exhibits a ferroelectric phase transition that is unaffected by the light-matter coupling. Bosonic dynamical mean-field theory provides a more accurate description and reveals that the photon-mediated interactions enhance the ferroelectric order and stabilize the ferroelectric phase.
- Published
- 2022
12. First-trimester abortion protocols in hospitals compared to office-based settings in Switzerland – a national survey study in Switzerland
- Author
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Samuel Martin Eckstein, Stefanie von Felten, Laura Perotto, Romana Brun, and Denise Vorburger
- Abstract
PurposeSimplified first-trimester abortion protocols are well established as they facilitate access to services and improve patient satisfaction without compromising safety. However, data on abortion protocols across Switzerland by facility type are lacking. Therefore, the first aim of this study was to analyse hospital-derived abortion protocols, as opposed to office-based protocols, across Switzerland in terms of their acceptance among women. The second aim was to assess abortion protocols and outcomes of specialised general practitioners (GPs) following simplified protocols.MethodsThis study consists of two parts. (i) A nationwide questionnaire was distributed among hospitals and private practices covering details of abortion protocols and numbers between April and July, 2019. The primary endpoint was the proportion of women undergoing an abortion after the first consultation at the chosen facility (adherence), regarding the complexity of abortion protocols in each setting. (ii) A retrospective study was conducted to analyse the outcomes of office-based institutions with simplified abortion procedures over a period of 10 years from January, 2008, to December, 2018. (BASEC-No. Req-2018-01031).Results (i) Office-based facilities showed less complex abortion protocols, resulting in a significantly higher probability of undergoing an abortion after the first consultation than hospitals. Their protocols allowed for a higher gestational age by medical means, and they offered mifepristone intake within the first consultation along with fewer staff members involved and a lower number of overall consultations. (ii) From 5,495 women, a total of 5,274 patients were included, of which the incidence of complications requiring surgery was at a low of 2.5%. ConclusionThis study highlights that simplified abortion protocols are crucial to ease access to abortion services, as represented by higher adherence in office-based facilities. Simplified protocols in abortion services are safe, and repetitive counselling and in-person visits should only be reserved for selected cases.
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- 2022
13. Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators
- Author
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Marion M. S. Barbeau, Martin Eckstein, Mikhail I. Katsnelson, Johan H. Mentink
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Physics ,QC1-999 - Abstract
In order to have a better understanding of ultrafast electrical control of exchange interactions in multi-orbital systems, we study a two-orbital Hubbard model at half filling under the action of a time-periodic electric field. Using suitable projection operators and a generalized time-dependent canonical transformation, we derive an effective Hamiltonian which describes two different regimes. First, for a wide range of non-resonant frequencies, we find a change of the bilinear Heisenberg exchange $J_{\textrm{ex}}$ that is analogous to the single-orbital case. Moreover we demonstrate that also the additional biquadratic exchange interaction $B_{\textrm{ex}}$ can be enhanced, reduced and even change sign depending on the electric field. Second, for special driving frequencies, we demonstrate a novel spin-charge coupling phenomenon enabling coherent transfer between spin and charge degrees of freedom of doubly ionized states. These results are confirmed by an exact time-evolution of the full two-orbital Mott-Hubbard Hamiltonian.
- Published
- 2019
- Full Text
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14. Dynamical phase transitions in the collisionless pre-thermal states of isolated quantum systems: theory and experiments
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Jamir, Marino, Martin, Eckstein, Matthew S, Foster, and Ana Maria, Rey
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Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Quantum Physics ,Statistical Mechanics (cond-mat.stat-mech) ,Strongly Correlated Electrons (cond-mat.str-el) ,Quantum Gases (cond-mat.quant-gas) ,Condensed Matter - Superconductivity ,General Physics and Astronomy ,FOS: Physical sciences ,Quantum Physics (quant-ph) ,Condensed Matter - Quantum Gases ,Condensed Matter - Statistical Mechanics - Abstract
We overview the concept of dynamical phase transitions in isolated quantum systems quenched out of equilibrium. We focus on non-equilibrium transitions characterized by an order parameter, which features qualitatively distinct temporal behaviour on the two sides of a certain dynamical critical point. Dynamical phase transitions are currently mostly understood as long-lived prethermal phenomena in a regime where inelastic collisions are incapable to thermalize the system. The latter enables the dynamics to substain phases that explicitly break detailed balance and therefore cannot be encompassed by traditional thermodynamics. Our presentation covers both cold atoms as well as condensed matter systems. We revisit a broad plethora of platforms exhibiting pre-thermal DPTs, which become theoretically tractable in a certain limit, such as for a large number of particles, large number of order parameter components, or large spatial dimension. The systems we explore include, among others, quantum magnets with collective interactions, $\phi^4$ quantum field theories, and Fermi-Hubbard models. A section dedicated to experimental explorations of DPTs in condensed matter and AMO systems connects this large variety of theoretical models., Comment: 37 pages; 10 figures; review article
- Published
- 2022
15. Control of Yu-Shiba-Rusinov States through a Bosonic Mode
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Helene Müller, Martin Eckstein, and Silvia Viola Kusminskiy
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Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,General Physics and Astronomy ,FOS: Physical sciences - Abstract
We investigate the impact of a bosonic degree of freedom on Yu-Shiba-Rusinov (YSR) states emerging from a magnetic impurity in a conventional superconductor. Starting from the Anderson impurity model, we predict that an additional p-wave conduction band channel opens up if a bosonic mode is coupled to the tunnelling between impurity and host, which implies an additional pair of odd-parity YSR states. The bosonic mode can be a vibrational mode or the electromagnetic field in a cavity. The exchange couplings in the two channels depend sensitively on the state of the bosonic mode (ground state, few quanta or classically driven Floquet state), which opens possibilities for phononics or photonics control of such systems, with a rich variety of ground and excited states.
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- 2022
- Full Text
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16. Vertex-based Diagrammatic Treatment of Light-Matter-Coupled Systems
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Aaram J. Kim, Katharina Lenk, Jiajun Li, Philipp Werner, and Martin Eckstein
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Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences ,General Physics and Astronomy - Abstract
We propose a diagrammatic Monte Carlo approach for general spin-boson models, which can be regarded as a generalization of the strong-coupling expansion for fermionic impurity models. The algorithm is based on a self-consistently computed three-point vertex and a stochastically sampled four-point vertex, and achieves convergence to the numerically exact result in a wide parameter regime. The performance of the algorithm is demonstrated with applications to a spin-boson model representing an emitter in a waveguide. As a function of the coupling strength, the spin exhibits a delocalization-localization crossover at low temperatures, signaling a qualitative change in the real-time relaxation. In certain parameter regimes, the response functions of the emitter coupled to the electromagnetic continuum can be described by an effective Rabi model with appropriately defined parameters. We also discuss the spatial distribution of the photon density around the emitter., 11 pages, 7 figures
- Published
- 2021
17. Quantum Boltzmann equation for strongly correlated electrons
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Antonio Picano, Martin Eckstein, and Jiajun Li
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,Distribution function ,Orders of magnitude (time) ,Quantum mechanics ,0103 physical sciences ,Boltzmann constant ,Quasiparticle ,symbols ,010306 general physics ,0210 nano-technology ,Anderson impurity model ,Quantum - Abstract
Collective orders and photo-induced phase transitions in quantum matter can evolve on timescales which are orders of magnitude slower than the femtosecond processes related to electronic motion in the solid. Quantum Boltzmann equations can potentially resolve this separation of timescales, but are often constructed within a perturbative framework. Here we derive a quantum Boltzmann equation which only assumes a separation of timescales (taken into account through the gradient approximation for convolutions in time), but is based on a non-perturbative scattering integral, and makes no assumption on the spectral function such as the quasiparticle approximation. In particular, a scattering integral corresponding to non-equilibrium dynamical mean-field theory is evaluated in terms of an Anderson impurity model in a non-equilibrium steady state with prescribed distribution functions. This opens the possibility to investigate dynamical processes in correlated solids with quantum impurity solvers designed for the study of non-equilibrium steady states., 11 pages, 3 figures
- Published
- 2021
18. Accelerated gap collapse in a Slater antiferromagnet
- Author
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Martin Eckstein and Antonio Picano
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Physics ,education.field_of_study ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Hubbard model ,Truncation ,Population ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Nonlinear system ,Thermalisation ,Orders of magnitude (time) ,0103 physical sciences ,Relaxation (physics) ,010306 general physics ,0210 nano-technology ,education - Abstract
We study the melting of long-range antiferromagnetic order in the Hubbard model after an interaction quench, using non-equilibrium dynamical mean-field theory. From previous studies, the system is known to quickly relax into a prethermal symmetry-broken state. Using a convergent truncation of the memory integrals in the Kadanoff Baym equations, we unravel the subsequent relaxation dynamics of this state over several orders of magnitude in time. At long times, the prethermal state can be characterized by a single slow variable which is related to the conduction band population. The dynamics of this variable does not follow the paradigmatic steady relaxation of pre-thermal states: It is highly nonlinear, with a pronounced speedup once the gap falls below a certain value. This behavior indicates that non-thermal order can be self-stabilized on some timescale. It is not reproduced using simple Fermi's golden rule estimate for the evolution of the conduction band population., 11 pages, 5 figures
- Published
- 2021
19. Electronic and fluctuation dynamics following a quench to the superconducting phase
- Author
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Martin Eckstein and Christopher Stahl
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Superconductivity ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,Degrees of freedom (physics and chemistry) ,FOS: Physical sciences ,Observable ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Superconductivity ,Pairing ,0103 physical sciences ,Dissipative system ,Quasiparticle ,010306 general physics ,0210 nano-technology ,Pseudogap - Abstract
We investigate the dynamics of superconducting fluctuations in the attractive three-dimensional Hubbard model after a quench from the disordered phase to the ordered regime. While the long time evolution is well understood in terms of dissipative time-dependent Ginzburg-Landau models with unstable potentials, early times are more demanding due to the inseparable dynamics of the pairing fluctuations and the electronic quasiparticles. Our simulation using the time-dependent fluctuation exchange approximation treat both degrees of freedom on the same footing and reveal a non-thermal electronic regime causing a non-monotonous growth of the fluctuations. This feature is not directly captured from the Ginzburg-Landau theory, but nevertheless remains observable beyond the thermalization time of the electrons. We further explore how the growth of the order parameter fluctuations leads to an opening of a pseudo-gap in the electronic spectrum, and identify Andreev reflections as the dominant mechanism behind the gap opening., Comment: 8 pages, 7 figures
- Published
- 2021
20. Effective theory of lattice electrons strongly coupled to quantum electromagnetic fields
- Author
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Jiajun Li, Lukas Schamriß, and Martin Eckstein
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences - Abstract
Recent experiments have revealed the tantalizing possibility of fabricating lattice electronic systems strongly coupled to quantum fluctuations of electromagnetic fields, e.g., by means of geometry confinement from a cavity or artificial gauge fields in quantum simulators. In this work, we develop a high-frequency expansion to construct the effective models for lattice electrons strongly coupled to a continuum of off-resonant photon modes with arbitrary dispersion. The theory is nonperturbative in the light-matter coupling strength, and is therefore particularly suitable for the ultrastrong light-matter coupling regime. Using the effective models, we demonstrate how the dispersion and topology of the electronic energy bands can be tuned by the cavity. In particular, quasi-one-dimensional physics can emerge in a two-dimensional square lattice due to a spatially anisotropic band renormalization, and a topologically nontrivial anomalous quantum Hall state can be induced in a honeycomb lattice when the cavity setup breaks time-reversal symmetry. We also demonstrate that the photon-mediated interaction induces an unconventional superconducting paired phase distinct from the pair-density-wave state discussed in models with truncated light-matter coupling. Finally, we study a realistic setup of a Fabry-P\'{e}rot cavity. Our work provides a systematic framework to explore the emergent phenomena due to strong light-matter coupling and points out new directions of engineering orders and topological states in solids.
- Published
- 2021
21. Effects of frustration on the nonequilibrium dynamics of photoexcited lattice systems
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Nikolaj Bittner, Martin Eckstein, Denis Golež, and Philipp Werner
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Physics ,education.field_of_study ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Hubbard model ,media_common.quotation_subject ,Population ,Relaxation (NMR) ,FOS: Physical sciences ,Frustration ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Square lattice ,Condensed Matter - Strongly Correlated Electrons ,Lattice (order) ,0103 physical sciences ,Density of states ,Condensed Matter::Strongly Correlated Electrons ,Hexagonal lattice ,010306 general physics ,0210 nano-technology ,education ,media_common - Abstract
We theoretically investigate the effects of the lattice geometry on the nonequilibrium dynamics of photo-excited carriers in a half-filled two-dimensional Hubbard model. Using a nonequilibrium generalization of the dynamical cluster approximation, we compare the relaxation dynamics in lattices which interpolate between the triangular lattice and square lattice configuration and thus reveal the role of the geometric frustration in these strongly correlated nonequilibrium systems. In particular, we show that the cooling effect resulting from the disordering of the spin background is less effective in the triangular case because of the frustration. This manifests itself in a longer relaxation time of the photo-doped population, as measured by the time-resolved photo-emission signal, and a higher effective temperature of the photo-doped carriers in the non-thermal steady state after the intra-Hubbard-band thermalization., Comment: 10 pages, 5 figures
- Published
- 2020
22. Simulation of time-dependent resonant inelastic X-ray scattering using non-equilibrium dynamical mean-field theory
- Author
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Philipp Werner and Martin Eckstein
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Scattering ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Signal ,Computational physics ,Pulse (physics) ,Resonant inelastic X-ray scattering ,Condensed Matter - Strongly Correlated Electrons ,Impurity ,0103 physical sciences ,Path (graph theory) ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We develop a framework to evaluate the time-dependent resonant inelastic X-ray scattering (RIXS) signal with the use of non-equilibrium dynamical mean field theory simulations. The approach is based on the solution of a time-dependent impurity model which explicitly incorporates the probe pulse. It avoids the need to compute four-point correlation functions, and can in principle be combined with different impurity solvers. This opens a path to study time-resolved RIXS processes in multi-orbital systems. The approach is exemplified with a study of the RIXS signal of a melting Mott antiferromagnet., 11 pages, 6 figures
- Published
- 2020
23. η -paired superconducting hidden phase in photodoped Mott insulators
- Author
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Denis Golez, Martin Eckstein, Philipp Werner, and Jiajun Li
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Superconductivity ,Physics ,Hubbard model ,Condensed matter physics ,Mott insulator ,Exchange interaction ,02 engineering and technology ,Conductivity ,021001 nanoscience & nanotechnology ,01 natural sciences ,Optical conductivity ,Condensed Matter - Strongly Correlated Electrons ,Metastability ,Phase (matter) ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
We show that a metastable $\eta$--pairing superconducting phase can be induced by photodoping doublons and holes into a strongly repulsive fermionic Hubbard model. The doublon-hole condensate originates from an intrinsic doublon-hole exchange interaction and does not rely on the symmetry of the half-filled Hubbard model. It extends over a wide range of doublon densities and effective temperatures. Different non-equilibrium protocols to realize this state are proposed and numerically tested. We also study the optical conductivity in the superconducting phase, which exhibits ideal metallic behavior, i.e., a delta function at zero-frequency in the conductivity, in conjunction with a negative conductivity at large frequencies. These characteristic optical properties can provide a fingerprint of the $\eta$-pairing phase in pump-probe experiments., Comment: 12 pages
- Published
- 2020
24. Nonequilibrium steady-state theory of photodoped Mott insulators
- Author
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Martin Eckstein and Jiajun Li
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Mott insulator ,FOS: Physical sciences ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Relaxation (physics) ,Transient (oscillation) ,Statistical physics ,Nonequilibrium steady state ,010306 general physics ,0210 nano-technology ,Excitation ,Physical quantity - Abstract
Photodoped states are widely observed in laser-excited Mott insulators, in which charge excitations are quickly created and can exist beyond the duration of the external driving. Despite the fruitful experimental explorations, theoretical studies on the microscopic models face the challenge to simultaneously deal with exponentially separated time scales, especially in multi-band systems, where the long-time behaviors are often well beyond the reach of state-of-the-art numerical tools. Here, we address this difficulty by introducing a steady-state description of photodoped Mott insulators using an open-system setup, where the photodoped system is stabilized as a non-equilirium steady-state (NESS) by a weak external driving. Taking advantage of the stationarity, we implement and discuss the details of an efficient numerical tool using the steady-state Dynamical Mean-Field Theory (DMFT), combined with the non-crossing approximation (NCA). We demonstrate that these stationary photodoped states exhibit the same properties of their transient counterparts, while being solvable with reasonable computational efforts. Furthermore, they can be parametrized by just few physical quantities, including the effective temperature and the density of charge excitations, which confirms the universal nature of photodoped states indeed independent of the excitation protocols. As a first application, we consider the stationary photodoped states in a two-band Hubbard model with intertwined spin-and-orbital ordering and find a family of hidden phases unknown from the previous studies, implying an apparently unexplored time regime of the relaxation of the intertwined orders.
- Published
- 2020
25. Quantum to classical crossover of Floquet engineering in correlated quantum systems
- Author
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Fabian Künzel, Jiajun Li, Michael A. Sentef, and Martin Eckstein
- Subjects
Physics ,Floquet theory ,Coupling ,Strongly Correlated Electrons (cond-mat.str-el) ,Atomic Physics (physics.atom-ph) ,Crossover ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,3. Good health ,Physics - Atomic Physics ,Condensed Matter - Strongly Correlated Electrons ,Quantum mechanics ,0103 physical sciences ,Strong coupling ,Mathematics::Metric Geometry ,010306 general physics ,0210 nano-technology ,Quantum - Abstract
Light-matter coupling involving classical and quantum light offers a wide range of possibilities to tune the electronic properties of correlated quantum materials. Two paradigmatic results are the dynamical localization of electrons and the ultrafast control of spin dynamics, which have been discussed within classical Floquet engineering and in the deep quantum regime where vacuum fluctuations modify the properties of materials. Here we discuss how these two extreme limits are interpolated by a cavity which is driven to the excited states. In particular, this is achieved by formulating a Schrieffer-Wolff transformation for the cavity-coupled system, which is mathematically analogous to its Floquet counterpart. Some of the extraordinary results of Floquet-engineering, such as the sign reversal of the exchange interaction or electronic tunneling, which are not obtained by coupling to a dark cavity, can already be realized with a single-photon state (no coherent states are needed). The analytic results are verified and extended with numerical simulations on a two-site Hubbard model coupled to a driven cavity mode. Our results generalize the well-established Floquet-engineering of correlated electrons to the regime of quantum light. It opens up a new pathway of controlling properties of quantum materials with high tunability and low energy dissipation., Comment: 20 pages, 11 figures
- Published
- 2020
26. Photoenhanced excitonic correlations in a Mott insulator with nonlocal interactions
- Author
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Denis Golež, Nikolaj Bittner, Martin Eckstein, and Philipp Werner
- Subjects
Condensed Matter::Quantum Gases ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,Condensed Matter::Other ,Thermodynamic equilibrium ,Exciton ,Mott insulator ,Continuum (design consultancy) ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,Observable ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Photoexcitation ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Materials Science ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We investigate the effect of nonlocal interactions on the photodoped Mott insulating state of the two-dimensional Hubbard model using a nonequilibrium generalization of the dynamical cluster approximation. In particular, we compare the situation where the excitonic states are lying within the continuum of doublon-holon excitations to a setup where the excitons appear within the Mott gap. In the first case, the creation of nearest-neighbor doublon-holon pairs by excitations across the Mott gap results in enhanced excitonic correlations, but these excitons quickly decay into uncorrelated doublons and holons. In the second case, photoexcitation results in long-lived excitonic states. While in a low-temperature equilibrium state, excitonic features are usually not evident in single-particle observables such as the photoemission spectrum, we show that the photoexcited nonequilibrium system can exhibit in-gap states associated with the excitons. The comparison with exact-diagonalization results for small clusters allows us to identify the signatures of the excitons in the photoemission spectrum.
- Published
- 2020
27. Light-induced evaporative cooling of holes in the Hubbard model
- Author
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Philipp Werner, Gil Refael, Markus Müller, and Martin Eckstein
- Subjects
Electronic properties and materials ,Hubbard model ,Science ,General Physics and Astronomy ,Non-equilibrium thermodynamics ,02 engineering and technology ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,lcsh:Science ,Quantum ,Computer Science::Databases ,Physics ,Multidisciplinary ,Condensed matter physics ,Mott insulator ,General Chemistry ,021001 nanoscience & nanotechnology ,Dipole ,lcsh:Q ,0210 nano-technology ,Néel temperature ,Theoretical physics ,Evaporative cooler - Abstract
An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature. Strongly correlated Fermi liquids and symmetry-broken states could thus be produced by dipolar excitations. Using nonequilibrium dynamical mean field theory, we show that suitably designed chirped pulses may realize this cooling effect. In particular, we demonstrate the emergence of antiferromagnetic order in a system which is initially in a weakly correlated state above the maximum Néel temperature. Our work suggests a general strategy for inducing strong correlation phenomena in periodically modulated atomic gases in optical lattices or light-driven materials., Driven quantum many-body systems can host finite densities of quasiparticles with the potential to realise emergent behaviour that is distinct from the equilibrium state. Werner et al. propose a method to cool holes in a correlated system so that more exotic low-entropy phases can be reached.
- Published
- 2020
28. Dynamically induced doublon repulsion in the Fermi-Hubbard model probed by a single-particle density of states
- Author
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Martin Eckstein, C. Dutreix, Mikhail I. Katsnelson, E. A. Stepanov, Alexander I. Lichtenstein, V. N. Valmispild, University of Hamburg, Laboratoire Ondes et Matière d'Aquitaine (LOMA), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux (UB), University of Erlangen-Nuremberg, and Radboud university [Nijmegen]
- Subjects
Hubbard model ,Theory of Condensed Matter ,Ac field ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,02 engineering and technology ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,Particle density ,ComputingMilieux_MISCELLANEOUS ,Physics ,[PHYS]Physics [physics] ,Condensed Matter::Quantum Gases ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Fermion ,021001 nanoscience & nanotechnology ,symbols ,Density of states ,[PHYS.COND.CM-SCE]Physics [physics]/Condensed Matter [cond-mat]/Strongly Correlated Electrons [cond-mat.str-el] ,0210 nano-technology ,Hamiltonian (quantum mechanics) ,Fermi Gamma-ray Space Telescope - Abstract
We investigate the possibility to control dynamically the interactions between repulsively bound pairs of fermions (doublons) in correlated systems with off-resonant ac fields. We introduce an effective Hamiltonian that describes the physics of doublons up to the second-order in the high-frequency limit. It unveils that the doublon interaction, which is attractive in equilibrium, can be completely suppressed and then switched to repulsive by varying the power of the ac field. We show that the signature of the dynamical repulsion between doublons can be found in the single-fermion density of states averaged in time. Our results are further supported by nonequilibrium dynamical mean-field theory simulations for the half-filled Fermi-Hubbard model.
- Published
- 2020
29. Manipulating intertwined orders in solids with quantum light
- Author
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Jiajun Li and Martin Eckstein
- Subjects
Physics ,Floquet theory ,Superconductivity ,Quantum Physics ,Photon ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,General Physics and Astronomy ,FOS: Physical sciences ,Quantum entanglement ,01 natural sciences ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Quantum mechanics ,0103 physical sciences ,Thermodynamic limit ,010306 general physics ,Quantum Physics (quant-ph) ,Quantum ,Quantum fluctuation ,Coherence (physics) - Abstract
Intertwined orders exist ubiquitously in strongly correlated electronic systems and lead to intriguing phenomena in quantum materials. In this paper, we explore the unique opportunity of manipulating intertwined orders through entangling electronic states with quantum light. Using a quantum Floquet formalism to study the cavity-mediated interaction, we show the vacuum fluctuations effectively enhance the charge-density-wave correlation, giving rise to a phase with entangled electronic order and photon coherence, with putative superradiant behaviors in the thermodynamic limit. Furthermore, upon injecting even one single photon in the cavity, different orders, including $s$--wave and $\eta$--paired superconductivity, can be selectively enhanced. Our study suggests a new and generalisable pathway to control intertwined orders and create light-matter entanglement in quantum materials. The mechanism and methodology can be readily generalised to more complicated scenarios., Comment: 6 pages + appendix
- Published
- 2020
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30. Non-equilibrium Dynamical Mean-Field Theory
- Author
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Martin Eckstein
- Published
- 2020
31. Collective excitations of the U(1)-symmetric exciton insulator in a cavity
- Author
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Martin Eckstein and Katharina Lenk
- Subjects
Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Exciton ,FOS: Physical sciences ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Dipole ,Condensed Matter - Strongly Correlated Electrons ,Mean field theory ,0103 physical sciences ,Quasiparticle ,Coulomb ,010306 general physics ,0210 nano-technology ,Ground state ,Discrete symmetry - Abstract
We investigate the equilibrium state and the collective modes of an excitonic insulator (EI) in a Fabry-P\'erot cavity. In an EI, two bands of a semiconductor or semimetal spontaneously hybridize due to the Coulomb interaction between electrons and holes, leading to the opening of a gap. The coupling to the electromagnetic field reduces the symmetry of the system with respect to phase rotations of the excitonic order parameter from $U(1)$ to $Z_2$. While the reduction to a discrete symmetry would in general lead to a gapped phase mode and enhance the stability of the ordered phase, the coupling to the cavity leaves the mean-field ground state unaffected. Its energy remains invariant under $U(1)$ phase rotations, in spite of the lower $Z_2$ symmetry imposed by the cavity. In dipolar gauge, this can be traced back to the balancing of the linear light-matter coupling and the dipolar self-interaction at zero frequency. At nonzero frequency, however, the collective excitations do reflect the lower $Z_2$ symmetry, which shows that fluctuations beyond mean-field could play a crucial role in finding the true phase at finite temperature., Comment: 13 pages, 6 figures
- Published
- 2020
- Full Text
- View/download PDF
32. Ultrafast Mott transition driven by nonlinear electron-phonon interaction
- Author
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Jiajun Li, Martin Eckstein, and Francesco Grandi
- Subjects
Physics ,Phase transition ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Phonon ,Semiclassical physics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Resonance (particle physics) ,Mott transition ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Ultrashort pulse ,Quantum - Abstract
Nonlinear phononics holds the promise for controlling properties of quantum materials on the ultrashort timescale. Using nonequilibrium dynamical mean-field theory, we solve a model for the description of organic solids, where correlated electrons couple nonlinearly to a quantum phonon mode. Unlike previous works, we exactly diagonalize the local phonon mode within the noncrossing approximation to include the full phononic fluctuations. By exciting the local phonon in a broad range of frequencies near resonance with an ultrashort pulse, we show it is possible to induce a Mott insulator-to-metal phase transition. Conventional semiclassical and mean-field calculations, where the electron-phonon interaction decouples, underestimate the onset of the quasiparticle peak. This fact, together with the nonthermal character of the photoinduced metal, suggests a leading role of the phononic fluctuations and of the dynamic nature of the state in the vibrationally induced quasiparticle coherence.
- Published
- 2020
- Full Text
- View/download PDF
33. Analysis of the metallography parameters and residual stress induced when producing bolt holes in Inconel 718 alloy
- Author
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Marek Vrabeľ, Ildikó Maňková, and Martin Eckstein
- Subjects
0209 industrial biotechnology ,Materials science ,Structural material ,Mechanical Engineering ,Surface stress ,Mechanical engineering ,02 engineering and technology ,Turbine ,Industrial and Manufacturing Engineering ,Computer Science Applications ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,Material selection ,Control and Systems Engineering ,Residual stress ,Service life ,Inconel ,Software ,Surface integrity - Abstract
Inconel 718 is a structural material used to produce highly stressed rotating aero-engine components. Such components have to meet the most exacting requirements in terms of reliability and component service life. Bolt holes in rotating turbine and compressor discs are among the most highly stressed geometric features of jet engines. In-flight failure of these bolt holes may, in fact, result in the loss of the aircraft and imperilment of human lives. For this reason, the quality and reliability of hole-making are of utmost importance. The integrity and reliability of the machined engine component are the sole factors for which all efforts are taken for system of design, material selection, manufacturing and inspection of these rotating aero-engine components. This paper aims to contribute towards a safer production of bolt holes in highly stressed turbine discs made from nickel based super-alloy, which acts as a linking sequence between microstructural surface integrity and descriptive residual stress parameters. The magnitude of the residual stress was determined by means of combining two various methods, namely surface stress measurement by X-ray diffraction and hole-drilling, to achieve residual stress in the profile depth.
- Published
- 2018
34. Time-resolved photoemission spectroscopy on correlated electrons: Insights from dynamical mean-field theory
- Author
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Martin Eckstein
- Subjects
Condensed Matter::Quantum Gases ,Physics ,Radiation ,Condensed matter physics ,Photoemission spectroscopy ,Mott insulator ,02 engineering and technology ,Electronic structure ,Electron ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,7. Clean energy ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,Relaxation (physics) ,Condensed Matter::Strongly Correlated Electrons ,Charge transfer insulators ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Quantum ,Spectroscopy ,Spin-½ - Abstract
Time- and angular-resolved photoemission spectroscopy (trARPES) can directly probe the electronic structure of quantum materials out of equilibrium. This can shed light on the interaction of the electrons with spin, lattice, and orbital degrees of freedom, and help to unravel pathways towards novel out-of-equilibrium phases. Dynamical mean-field theory (DMFT) and its extensions provide a versatile toolbox to interpret such experiments through a theoretical simulation of the underlying microscopic processes. The approach can be applied both to Mott insulators and correlated metals, and it is formulated in terms of non-equilibrium Green's functions, which directly relate to the photoemission spectrum. This article reviews the theoretical description of trARPES within DMFT and related diagrammatic non-equilibrium Green's function techniques. Several applications are discussed, including the photo-induced melting of excitonic order, femtosecond relaxation processes in Mott insulators, and the manipulation of the electronic structure of Mott and charge transfer insulators using photo-doping and strong THz fields.
- Published
- 2021
35. Application of Discrete Wavelet Decomposition in Monitoring of Hole-making Inconel 718
- Author
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Martin Eckstein, Marek Vrabeľ, and Ildikó Maňková
- Subjects
0209 industrial biotechnology ,Engineering drawing ,Engineering ,Hardware_MEMORYSTRUCTURES ,business.product_category ,Profibus ,business.industry ,Drilling ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Signal ,Machine tool ,020901 industrial engineering & automation ,Wavelet ,Transformation (function) ,Control theory ,General Earth and Planetary Sciences ,Torque ,0210 nano-technology ,business ,Spiral ,General Environmental Science - Abstract
The paper describes an application of discrete wavelet decomposition of monitored signals from Profibus data originating from spindle and from the feed drive of machine tool. Discrete wavelet decomposition is a most efficient method to separate uniform signal pattern from disordered signal. It was demonstrated that - compared to the evolution of average spindle torque over the tool path - extracted signal variance from the spindle torque through application of wavelet transformation has a significantly higher correlation with maximum flank wear on the tool. Within the framework of tools and cutting conditions chosen in this work, this is true both for drilling with spiral drills and for finishing with face-cutting finishers.
- Published
- 2017
36. Intelligent Monitoring System for Zero-Defect Production of Irreplaceable Parts
- Author
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Martin Eckstein, Ladislav Vargovčík, Ildikó Maňková, and Marek Vrabeľ
- Subjects
Computer science ,business.industry ,Profibus ,media_common.quotation_subject ,Final product ,Scrap ,Data quality ,Zero Defects ,Data logger ,Production (economics) ,Quality (business) ,Process engineering ,business ,media_common - Abstract
Hole making process monitoring of irreplaceable parts is crucial in terms of waste production elimination. Defects on machined part do not directly affects its end user. Strict quality control regulations in all production levels ensure the required product quality. However, faulty parts increase production costs proportionally. These costs are included in the sale price for which end user purchases the product. In order to achieve a significant reduction of the waste production a new generation of sensors will be applied to obtain appropriate signals directly from the machine control unit. For the real time and effective signal processing, wavelet transformation and neural network approach will be used to identify changes of the cutting tool or machined surface. Such a proposed system has all necessary assumptions to reduce scrap production in manufacturing chain and thus reduce the price of final product. The paper describes a approach in real-time monitoring for drilling boltholes. In an experimental setup, process data origination from the CNC of a Sinumeric 840D, collected by an OPC-Server had been processed. Comparing OPC data logging, DAU data logging and profibus data logging with respect to data quality, sample rate and real-time behaviour, profibus data logging appears to be the favourable choice.
- Published
- 2019
37. Ultrafast electric field controlled spin correlations in the Hubbard model
- Author
-
Martin Eckstein and Nagamalleswararao Dasari
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Momentum ,Brillouin zone ,Condensed Matter - Strongly Correlated Electrons ,Ferromagnetism ,Electric field ,0103 physical sciences ,Antiferromagnetism ,Bloch oscillations ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
Highly intense electric field pulses can move the electronic momentum occupation in correlated metals over large portions of the Brillouin zone, leading to phenomena such as dynamic Bloch oscillations. Using the non-equilibrium fluctuation-exchange approximation for the two-dimensional Hubbard model, we study how such non-thermal electron-distributions drive collective spin and charge fluctuations. Suitable pulses can induce a highly anisotropic modification of the occupied momenta, and the corresponding spin dynamics results in a transient change from antiferromagnetic to anisotropic ferromagnetic correlations. To good approximation this behavior is understood in terms of an instantaneous response of the spin fluctuations to the single-particle properties, opposite to the conventional time-scale separation between spin and electron dynamics., Comment: 5 pages, 5 figures
- Published
- 2019
38. Revealing Hund's multiplets in Mott insulators under strong electric fields
- Author
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Nagamalleswararao Dasari, Jiajun Li, Martin Eckstein, and Philipp Werner
- Subjects
Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Mott insulator ,FOS: Physical sciences ,02 engineering and technology ,Electron ,Quantum Hall effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Paramagnetism ,Coupling (physics) ,Condensed Matter - Strongly Correlated Electrons ,Electric field ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Quantum tunnelling ,Spin-½ - Abstract
We investigate the strong-field dynamics of a paramagnetic two-band Mott insulator using real-time dynamical mean-field theory. A dielectric breakdown occurs due to many-body Landau-Zener tunnelling, with a threshold field determined by the gap. For a large range of fields, however, we predict that the tunnelling currents are small enough to allow the observation of field-induced localization of electrons, which becomes most strikingly evident in atomic-like local spin multiplets determined by the Hund's coupling $J$. This field-induced localization might provide a way of measuring the value of $J$ in correlated materials. It should be observable in transition metal oxides using time-resolved photo-emission spectroscopy or optical measurements in the presence of strong THz field transients., 7 pages and 7 figures
- Published
- 2019
39. Ultrafast Spin Dynamics in Photodoped Spin-Orbit Mott Insulator Sr2IrO4
- Author
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Andrea D. Caviglia, Jiajun Li, Marta Gibert, N Dasari, Stefano Gariglio, D. Afanasiev, T.H.M. Rasing, A. Gatilova, Alexey Kimel, B A Ivanov, Martin Eckstein, J.H. Mentink, and Dirk J. Groenendijk
- Subjects
Physics ,Kerr effect ,Hubbard model ,Condensed matter physics ,Spins ,Magnetism ,Mott insulator ,Physics::Optics ,General Physics and Astronomy ,01 natural sciences ,010305 fluids & plasmas ,Magnetization ,0103 physical sciences ,Phenomenological model ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics - Abstract
Ultrafast photodoping of the Mott insulators, possessing strong correlation between electronic and magnetic degrees of freedom, holds promise for launching an ultrafast dynamics of spins which cannot be described in terms of conventional models of ultrafast magnetism. Here we study the ultrafast laser-induced dynamics of the magnetic order in a novel spin-orbit Mott insulator Sr2IrO4 featuring an uncompensated pattern of antiferromagnetic spin ordering. Using the transient magneto-optical Kerr effect sensitive to the net magnetization, we reveal that photodoping by femtosecond laser pulses with photon energy above the Mott gap launches melting of the antiferromagnetic order seen as ultrafast demagnetization with a characteristic time of 300 fs followed by a sub-10-ps recovery. Nonequilibrium dynamical mean-field theory calculations based on the single-band Hubbard model confirm that ultrafast demagnetization is primarily governed by the laser-induced generation of electron-hole pairs, although the precise simulated time dependencies are rather different from the experimentally observed ones. To describe the experimental results, here we suggest a phenomenological model which is based on Onsager’s formalism and accounts for the photogenerated electron-hole pairs using the concepts of holons and doublons.
- Published
- 2019
40. Erratum: Ultrafast Doublon Dynamics in Photoexcited 1T−TaS2 [Phys. Rev. Lett. 120 , 166401 (2018)]
- Author
-
M. Kalläne, Ph. Werner, Y. Beyazit, Uwe Bovensiepen, Kai Rossnagel, Martin Eckstein, Ping Zhou, Florian Diekmann, Manuel Ligges, I. Avigo, Denis Golež, Hugo U. R. Strand, L. Stojchevska, and K. Hanff
- Subjects
Physics ,General Physics and Astronomy ,Atomic physics ,Ultrashort pulse - Published
- 2019
41. Time-resolved photoelectron spectroscopy of organic molecules in aqueous solutions
- Author
-
Johan Hummert, G. Reitsma, Evgenii Ikonnikov, Oleg Kornilov, Nicola Mayer, and Martin Eckstein
- Subjects
Aqueous solution ,Molar concentration ,Physics ,QC1-999 ,Relaxation (NMR) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,X-ray photoelectron spectroscopy ,Extreme ultraviolet ,0103 physical sciences ,Femtosecond ,Physics::Atomic and Molecular Clusters ,Physics::Chemical Physics ,010306 general physics ,0210 nano-technology ,Isomerization ,Excitation - Abstract
We use time-resolved photoelectron spectroscopy with wavelength-selected XUV femtosecond pulses to study photoinduced dynamics of organic molecules in solutions at millimolar concentrations. Upon electronic excitation we observe relaxation processes, such as excited state intramolecular proton transfer and trans-cis isomerization.
- Published
- 2019
42. Floquet DMFT Analysis of High Harmonic Generation in Mott Insulators
- Author
-
Yuta Murakami, Philipp Werner, and Martin Eckstein
- Subjects
Floquet theory ,Physics ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,business.industry ,Mott insulator ,Spectrum (functional analysis) ,FOS: Physical sciences ,Field strength ,Plateau (mathematics) ,Condensed Matter - Strongly Correlated Electrons ,Semiconductor ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,High harmonic generation ,Condensed Matter::Strongly Correlated Electrons ,Physics::Atomic Physics ,business ,Energy (signal processing) - Abstract
We study the high harmonic generation (HHG) in Mott insulators using Floquet dynamical mean-field theory (DMFT). We show that the main origin of the HHG in Mott insulators is the doublon-holon recombination, and that the character of the HHG spectrum differs depending on the field strength. In the weaker-field regime, the HHG spectrum shows a single plateau as in the HHG from gases, and its cut-off energy $\epsilon_{\rm cut}$ scales linearly with the field strength $E_0$ as $\epsilon_{\rm cut}=\Delta_{\rm gap} + \alpha E_0$, where $\Delta_{\rm gap}$ is the Mott gap. On the other hand, in the stronger-field regime, multiple plateaus emerge and the $m$-th cut-off scales as $\epsilon_{\rm cut,m}=U + m E_0$. We show that this difference originates from the different dynamics of the doublons and holons in the weak- and strong-field regimes. We also comment on the similarities and differences between HHG from Mott insulators and from semiconductors. This proceedings paper complements our recent work, Phys. Rev. Lett. 121, 057405 (2018), with additional results and analyses., Comment: 6 pages, proceedings of SCES2019(accepted)
- Published
- 2019
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- View/download PDF
43. Entropy-cooled nonequilibrium states of the Hubbard model
- Author
-
Jianju Li, Philipp Werner, Denis Golež, and Martin Eckstein
- Subjects
Physics ,Superconductivity ,Condensed Matter::Quantum Gases ,education.field_of_study ,Condensed matter physics ,Hubbard model ,Strongly Correlated Electrons (cond-mat.str-el) ,Population ,Non-equilibrium thermodynamics ,FOS: Physical sciences ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Superconductivity ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,education - Abstract
We show that the recently proposed cooling-by-doping mechanism allows one to efficiently prepare interesting nonequilibrium states of the Hubbard model. Using nonequilibrium dynamical mean field theory and a particle-hole symmetric setup with dipolar excitations to full and empty bands we produce cold photodoped Mott insulating states with a sharp Drude peak in the optical conductivity, a superconducting state in the repulsive Hubbard model with an inverted population, and η -paired states in systems with a large density of doublons and holons. The reshuffling of entropy into full and empty bands not only provides an efficient cooling mechanism, it also allows one to overcome thermalization bottlenecks and slow dynamics that have been observed in systems cooled by the coupling to boson baths.
- Published
- 2019
- Full Text
- View/download PDF
44. Adiabatic Preparation of a Correlated Symmetry‐Broken Initial State with the Generalized Kadanoff–Baym Ansatz
- Author
-
Riku Tuovinen, Michael Schüler, Denis Golež, Philipp Werner, Michael A. Sentef, and Martin Eckstein
- Subjects
010302 applied physics ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Crystal system ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Equilibrium phase ,Condensed Matter - Strongly Correlated Electrons ,Quantum mechanics ,0103 physical sciences ,0210 nano-technology ,Adiabatic process ,Wave function ,Ansatz - Abstract
A fast time propagation method for nonequilibrium Green's functions based on the generalized Kadanoff--Baym Ansatz (GKBA) is applied to a lattice system with a symmetry-broken equilibrium phase, namely an excitonic insulator. The adiabatic preparation of a correlated symmetry-broken initial state from a Hartree--Fock wave function within GKBA is assessed by comparing with a solution of the imaginary-time Dyson equation. We find that it is possible to reach a symmetry-broken correlated initial state with nonzero excitonic order parameter by the adiabatic switching procedure. We discuss under which circumstances this is possible in practice within reasonably short switching times., 10 pages, 5 figures, Progress in Nonequilibrium Green's Functions VII proceedings
- Published
- 2019
- Full Text
- View/download PDF
45. Dynamics of photodoped charge transfer insulators
- Author
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Philipp Werner, Denis Golež, Lewin Boehnke, and Martin Eckstein
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,law.invention ,Complex materials ,Renormalization ,Condensed Matter - Strongly Correlated Electrons ,law ,Condensed Matter::Superconductivity ,0103 physical sciences ,Charge transfer insulators ,Cuprate ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We study the dynamics of charge-transfer insulators after photo-excitation using the three-band Emery model and a nonequilibrium extension of Hartree-Fock+EDMFT and GW+EDMFT. While the equilibrium properties are accurately reproduced by the Hartree-Fock treatment of the full $p$ bands, dynamical correlations are essential for a proper description of the photo-doped state. The insertion of doublons and holons leads to a renormalization of the charge transfer gap %and $p$ bands and to a substantial broadening of the bands. We calculate the time-resolved photoemission spectrum and optical conductivity and find qualitative agreement with experiments. Our formalism enables the realistic description of nonequilibrium phenomena in a large class of charge-transfer insulators, and provides a tool to explore the optical manipulation of interaction and correlation effects., Comment: 5 pages, 5 figures
- Published
- 2019
- Full Text
- View/download PDF
46. Noise correlations in time- and angle-resolved photoemission spectroscopy
- Author
-
Christopher Stahl and Martin Eckstein
- Subjects
Superconductivity ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Photoemission spectroscopy ,Scattering ,Dephasing ,FOS: Physical sciences ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Pairing ,0103 physical sciences ,Cooper pair ,010306 general physics ,0210 nano-technology - Abstract
In time-resolved photoemission experiments, more than one electron can be emitted from the solid by a single ultra-short pulse. We theoretically demonstrate how correlations between the momenta of outgoing electrons relate to time-dependent two-particle correlations in the solid. This can extend the scope of time- and angular-resolved photoemission spectroscopy to probe superconducting and charge density fluctuations in systems without long-range order, and to reveal their dynamics independent of the electronic gap and thus unrestricted by the energy-time uncertainty. The proposal is illustrated for superconductivity in a BCS model. An impulsive perturbation can quench the gap on ultrafast timescales, while non-equilibrium pairing correlations persist much longer, even when electron-electron scattering beyond mean-field theory is taken into account. There is thus a clear distinction between a dephasing of the Cooper pairs and the thermalization into the normal state. While a measurement of the gap would be blind to such pairing correlations, they can be revealed by the angular correlations in photoemission., 7 pages, 2 figures
- Published
- 2019
- Full Text
- View/download PDF
47. Multiband nonequilibrium G W + EDMFT formalism for correlated insulators
- Author
-
Philipp Werner, Denis Golež, and Martin Eckstein
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Ab initio ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Optical conductivity ,Spectral line ,3. Good health ,Photoexcitation ,Renormalization ,Condensed Matter - Strongly Correlated Electrons ,Dipole ,Condensed Matter::Superconductivity ,0103 physical sciences ,Cuprate ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
We study the dynamics of charge-transfer insulators after a photo-excitation using the three-band Emery model which is relevant for the description of cuprate superconductors. We provide a detailed derivation of the nonequilibrium extension of the multi-band GW+EDMFT formalism and the corresponding downfolding procedure. The Peierls construction of the electron-light coupling is generalized to the multi-band case resulting in a gauge invariant combination of the Peierls intra-band acceleration and dipolar intra-band transitions. We apply the formalism to the study of momentum-dependent (inverse) photo-emission spectra and optical conductivities. The time-resolved spectral function shows a strong renormalization of the charge-transfer gap and a substantial broadening of some of the bands. While the upper Hubbard band exhibits a momentum-dependent broadening, an almost rigid band shift is observed for the ligand bands. The inverse photo-emission spectrum reveals that the inclusion of the non-local and inter-band charge fluctuations lead to a very fast relaxation of holes into the lower Hubbard band. Consistent with the changes in the spectral function, the optical conductivity shows a renormalization of the charge-transfer gap, which is proportional to the photo-doping. The details of the photo-induced changes strongly depend on the dipolar matrix elements, which calls for an ab-initio determination of these parameters., Comment: Substantial updates on a discussion of light-matter coupling and corrected results for optical conductivity
- Published
- 2019
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48. Quantum Simulation Meets Nonequilibrium Dynamical Mean-Field Theory: Exploring the Periodically Driven, Strongly Correlated Fermi-Hubbard Model
- Author
-
Philipp Werner, Kilian Sandholzer, Frederik Görg, Michael Messer, Tilman Esslinger, Martin Eckstein, Yuta Murakami, Rémi Desbuquois, and Joaquin Minguzzi
- Subjects
Physics ,Optical lattice ,Quantum Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Time evolution ,FOS: Physical sciences ,General Physics and Astronomy ,Quantum simulator ,Non-equilibrium thermodynamics ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Amplitude ,Quantum Gases (cond-mat.quant-gas) ,Quantum electrodynamics ,0103 physical sciences ,symbols ,Quantum Physics (quant-ph) ,010306 general physics ,Hamiltonian (quantum mechanics) ,Condensed Matter - Quantum Gases ,Excitation - Abstract
Physical Review Letters, 123 (19), ISSN:0031-9007, ISSN:1079-7114
- Published
- 2018
49. Control of competing superconductivity and charge order by nonequilibrium currents
- Author
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Jiajun Li, Martin Eckstein, and Anne Matthies
- Subjects
Thermal equilibrium ,Superconductivity ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Hubbard model ,Condensed matter physics ,Scattering ,Condensed Matter - Superconductivity ,FOS: Physical sciences ,Non-equilibrium thermodynamics ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Thermal ,Electric current ,010306 general physics ,0210 nano-technology - Abstract
We study the competing charge-density-wave and superconducting order in the attractive Hubbard model under a voltage bias, using steady-state non-equilibrium dynamical mean-field theory. We show that the charge-density-wave is suppressed in a current-carrying non-equilibrium steady state. This effect is beyond a simple Joule-heating mechanism and a "supercooled" metallic state is stabilized at a non-equilibrium temperature lower than the equilibrium superconducting $T_c$. On the other hand, a current-carrying superconducting state is always in equilibrium. It is not subject to the same non-thermal suppression, and can therefore nucleate out of the supercooled metal, e.g. in a resistive switching experiment. The fact that an electric current can change the relative stability of different phases compared to thermal equilibrium, even when a system appears locally thermal due to electron-eletron scattering, provides a general perspective to control intertwined orders out of equilibrium., 5 pages; 4 figures
- Published
- 2018
50. Femtosecond Extreme Ultraviolet Photoelectron Spectroscopy of Organic Molecules in Aqueous Solution
- Author
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Oleg Kornilov, G. Reitsma, Evgenii Ikonnikov, Johan Hummert, Martin Eckstein, and Nicola Mayer
- Subjects
Aqueous solution ,Materials science ,Valence (chemistry) ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Molecular dynamics ,X-ray photoelectron spectroscopy ,Intramolecular force ,Femtosecond ,Molecule ,General Materials Science ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Time-resolved valence photoelectron spectroscopy is an established tool for studies of ultrafast molecular dynamics in the gas phase. Here we demonstrate time-resolved XUV photoelectron spectroscopy from dilute aqueous solutions of organic molecules, paving the way to application of this method to photodynamics studies of organic molecules in natural environments, which so far have only been accessible to all-optical transient spectroscopies. We record static and time-resolved photoelectron spectra of a sample molecule, quinoline yellow WS, analyze its electronic structure, and follow the relaxation dynamics upon excitation with 400 nm pulses. The dynamics exhibit three time scales, of which a 250 ± 70 fs time scale is attributed to solvent rearrangement. The two longer time scales of 1.3 ± 0.4 and 90 ± 20 ps can be correlated to the recently proposed ultrafast excited-state intramolecular proton transfer in a closely related molecule, quinophthalone.
- Published
- 2018
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