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Lars Edelmann,1 Marike Hempel,2 Natalia Podsiadlo,1 Nora Schweizer,2 Cindy Tong,3 Thibaut Galvain,4 Hannah Taylor,5 Michael Schüler1 1Kantonsspital Münsterlingen, Münsterlingen, 8596, Switzerland; 2Johnson & Johnson AG, Zug, 6300, Switzerland; 3Johnson and Johnson Medical Devices, Somerville, NJ, USA; 4Johnson and Johnson Medical, Issy les Moulineaux, France; 5Johnson & Johnson Medical Limited, Berkshire, UKCorrespondence: Lars Edelmann, Klinik für Orthopädie und Traumatologie, Kantonsspital Münsterlingen, Spitalcampus 1, Münsterlingen, 8596, Switzerland, Tel +41-71-686-20 50, Fax +41-71-686-20 23, Email lars.edelmann@stgag.chPurpose: Total knee and hip arthroplasties (TKA and THA) are common surgical procedures in Switzerland and worldwide. Alongside increasing demand for these procedures, many providers have adopted enhanced recovery programs (ERPs) that aim to optimize recovery after these surgeries. We evaluated the impact of implementing a Patient Pathway Optimization (PPO) program designed around ERP principles for patients undergoing TKA or THA in a Swiss Cantonal hospital. The primary objective was to determine whether PPO implementation for patients undergoing TKA or THA reduced length of stay (LOS) during index hospitalization. Additional study outcomes were hospital inpatient costs, rate of complications and readmissions, and patient discharge destination.Methods: This was a retrospective, observational study comparing outcomes before and after PPO implementation for patients who underwent primary TKA or THA from 2014 to 2019. The PPO program modified the care pathway and implemented five ERP principles (preoperative patient education, pre-operative physiotherapy, local infiltration analgesia, early mobilization, and oral analgesia). Hospital electronic medical record and billing data were used for the analysis.Results: After implementation of PPO, LOS was shorter compared with the pre-PPO period (reduction of 2.5 and 2.4 days in TKA and THA cohorts, respectively, both p < 0.001). Mean inpatient costs per patient were also reduced following PPO (decrease of USD2016 [p = 0.015] and USD340 [p = 0.54] for TKA and THA cohorts, respectively). There were no observed increases in readmissions or complications after PPO implementation in either the TKA or THA cohort. More patients in the post-PPO groups were discharged to home vs an alternative health-care setting than in the pre-PPO groups (TKA, 83.8% vs 68.4% [p = 0.07]; THA, 80.4% vs 73.9%, [p = 0.31]).Conclusion: Patient pathway optimization and implementation of additional enhanced recovery principles for TKA and THA may benefit both health systems and patients, by reducing LOS and costs without increases in complications or readmissions.Keywords: enhanced recovery program, total hip replacement, total knee replacement, joint replacement, costs

Resonant inelastic X-ray scattering (RIXS) can probe localized excitations at selected atoms in materials, including particle-hole transitions between the valence and conduction bands. These transitions are governed by fundamental properties of the corresponding Bloch wave-functions, including orbital and magnetic degrees of freedom, and quantum geometric properties such as the Berry curvature. In particular, orbital angular momentum (OAM), which is closely linked to the Berry curvature, can exhibit a nontrivial momentum dependence. We demonstrate how information on such OAM textures can be extracted from the circular dichroism in RIXS. Based on accurate modeling with first-principles treatment of the key ingredient -- the light-matter interaction -- we simulate dichroic RIXS spectra for the prototypical transition metal dichalcogenide MoSe$_2$ and the two-dimensional topological insulator 1T$^\prime$-MoS$_2$. Guided by an intuitive picture for the optical selection rules, we discuss how the momentum-dependent OAM manifests itself in the dichroic RIXS signal if one controls the momentum transfer. Our calculations are performed for typical experimental geometries and parameter regimes, and demonstrate the possibility of observing the predicted circular dichroism in forthcoming experiments. Thus, our work establishes a new avenue to observing Berry curvature and topological states in quantum materials., 11 pages, 5 figues

High-harmonic generation (HHG) in solids is a fundamental nonlinear phenomenon, which can be efficiently controlled by modifying system parameters such as doping-level and temperature. In order to correctly predict the dependence of HHG on these parameters, consistent theoretical formulation of the light-matter coupling is crucial. Recently, contributions to the current that are often missing in the HHG analysis based on the semiconductor Bloch equations have been pointed out [J. Wilhelm, et.al. PRB 103 125419 (2021)]. In this paper, by systematically analyzing the doping and gap-size dependence of HHG in gapped graphene, we discuss the practical impact of such terms. In particular, we focus on the role of the current $J_{\rm ra}^{(2)}$, which originates from the change of the intraband dipole via interband transition. When the gap is small and the system is close to half filling, intraband and interband currents mostly cancel, thus suppressing the HHG signal - an important property that is broken when neglecting $J_{\rm ra}^{(2)}$. Furthermore, without $J_{\rm ra}^{(2)}$, the doping and gap-size dependence of HHG becomes qualitatively different from the full evaluation. Our results demonstrate the importance of the consistent expression of the current to study the parameter dependence of HHG for the small gap systems., Comment: 13 pages, 8 figures

We investigate topological signatures in the short-time non-equilibrium dynamics of symmetry protected topological (SPT) systems starting from initial states which break the protecting symmetry. Na\"ively, one might expect that topology loses meaning when a protecting symmetry is broken. Defying this intuition, we illustrate, in an interacting Su-Schrieffer-Heeger (SSH) model, how this combination of symmetry breaking and quench dynamics can give rise to both single-particle and many-body signatures of topology. From the dynamics of the symmetry broken state, we find that we are able to dynamically probe the equilibrium topological phase diagram of a symmetry respecting projection of the post-quench Hamiltonian. In the ensemble dynamics, we demonstrate how spontaneous symmetry breaking (SSB) of the protecting symmetry can result in a quantized many-body topological `invariant' which is not pinned under unitary time evolution. We dub this `dynamical many-body topology' (DMBT). We show numerically that both the pure state and ensemble signatures are remarkably robust, and argue that these non-equilibrium signatures should be quite generic in SPT systems, regardless of protecting symmetries or spatial dimension., Comment: 13 pages + appendix; 5 figures

Electron-phonon interaction and related self-energy are fundamental to both the equilibrium properties and non-equilibrium relaxation dynamics of solids. Although electron-phonon interaction has been suggested by various time-resolved measurements to be important for the relaxation dynamics of graphene, the lack of energy- and momentum-resolved self-energy dynamics prohibits direct identification of the role of specific phonon modes in the relaxation dynamics. Here by performing time- and angle-resolved photoemission spectroscopy measurements on a Kekul\'e-ordered graphene with folded Dirac cones at the $\Gamma$ point, we have succeeded in resolving the self-energy effect induced by coupling of electrons to two phonons at $\Omega_1$ = 177 meV and $\Omega_2$ = 54 meV and revealing its dynamical change in the time domain. Moreover, these strongly coupled phonons define energy thresholds, which separate the hierarchical relaxation dynamics from ultrafast, fast to slow, thereby providing direct experimental evidence for the dominant role of mode-specific phonons in the relaxation dynamics, Comment: Kekul\'e-ordered graphene 2: Self-energy dynamics and phonon threshold effect revealed by time- and angle-resolved photoemission spectroscopy

Background Patients are becoming increasingly more independent and self-determined, in addition to having shorter post-operative hospitalization. This is why it is more important than ever to actively involve patients in the follow-up treatment. The question arises as to whether post-operative rehabilitation can be improved with modern devices. Methods As part of a prospective study, the post-operative mobilization was recorded and analyzed by Fitbit®-activity-trackers between 05/2016 and 08/2017 in 100 patients who received a THA. 50 men (O 70.6y) and 50 women (O 71.1y) were included. Furthermore, the patients were interviewed about their acceptance of the Fitbit®-wristband. Results The average hospital stay was 7.98 days (SD ± 1.76). The number of steps on the first post-operative day was 712 (SD ± 617). On average (during total hospitalization), 1528 (SD ± 1076) steps were completed daily. One day before discharge, the average number of steps was 2165 (SD ± 1570) on that particular day. There were no gender differences in age and pre-operative Harris hip scores (♂55.3 vs. ♀53.9). Also, there were no statistically significant differences in the number of steps on the first postoperative day (♂745 vs. ♀678). A statistically significant result can be found in the number of steps prior to discharge: on this day, the men took 2483 and the women 1846 steps (p = 0.04). 42% of our patients own a modern smartphone and are able to operate software applications. 52% of the patients found the activity tracker to be motivating, 65% were open to new technologies (e.g. activity trackers) in the hospital. 14% did not check at all or only queried their wristband data once a day, 65% queried 2-4 times/day, and 21% retrieved the data >5 times/day. Discussion On average, 1528 steps were completed daily. In a comparison of the men and women, the men were only able to demonstrate significantly more steps than the women on the day prior to discharge. The men had significantly shorter hospital stays than the women. The younger the patients, the more mobile they were. A majority of patients are familiar with and/or interested in new technologies. This interest and curiosity should be consciously used for integration in the post-operative treatment.

We study the different ways of introducing light-matter interaction in first-principle tight-binding (TB) models. The standard way of describing optical properties is the velocity gauge, defined by linear coupling to the vector potential. In finite systems a transformation to represent the electromagnetic radiation by the electric field instead is possible, albeit subtleties arise in periodic systems. The resulting dipole gauge is a multi-orbital generalization of Peierl's substitution. In this work, we investigate accuracy of both pathways, with particular emphasis on gauge invariance, for TB models constructed from maximally localized Wannier functions. Focusing on paradigmatic two-dimensional materials, we construct first-principle models and calculate the response to electromagnetic fields in linear response and for strong excitations. Benchmarks against fully converged first-principle calculations allow for ascertaining the accuracy of the TB models. We find that the dipole gauge provides a more accurate description than the velocity gauge in all cases. The main deficiency of the velocity gauge is an imperfect cancellation of paramagnetic and diamagnetic current. Formulating a corresponding sum rule however provides a way to explicitly enforce this cancellation. This procedure corrects the TB models in the velocity gauge, yielding excellent agreement with dipole gauge and thus gauge invariance., Comment: 13 pages, 6 figures

We report on the dynamical formation of exceptional degeneracies in basic correlation functions of non-integrable one- and two-dimensional systems quenched to the vicinity of a critical point. Remarkably, fine-tuned semi-metallic points in the phase diagram of the considered systems are thereby promoted to topologically robust non-Hermitian (NH) nodal phases emerging in the coherent long-time evolution of a dynamically equilibrating system. In the framework of non-equilibrium Green's function methods within the conserving second Born approximation, we predict observable signatures of these novel NH nodal phases in simple spectral functions as well as in the time-evolution of momentum distribution functions.

Migdal-Eliashberg theory describes the properties of the normal and superconducting states of electron-phonon-mediated superconductors based on a perturbative treatment of the electron-phonon interactions. It is necessary to include both electron and phonon self-energies self-consistently in Migdal-Eliashberg theory in order to match numerically exact results from determinantal quantum Monte Carlo in the adiabatic limit. In this work we provide a method to obtain the real-axis solutions of the Migdal-Eliashberg equations with electron and phonon self-energies calculated self-consistently. Our method avoids the typical challenge of computing cumbersome singular integrals on the real axis and is numerically stable and exhibits fast convergence. Analyzing the resulting real-frequency spectra and self-energies of the two-dimensional Holstein model, we find that self-consistently including the lowest-order correction to the phonon self-energy significantly affects the solution of the Migdal-Eliashberg equations. The calculation captures the broadness of the spectral function, renormalization of the phonon dispersion, enhanced effective electron-phonon coupling strength, minimal increase in the electron effective mass, and the enhancement of superconductivity which manifests as a superconducting ground state despite strong competition with charge-density-wave order. We discuss surprising differences in two common definitions of the electron-phonon coupling strength derived from the electron mass and the density of states, quantities which are accessible through experiments such as angle-resolved photoemission spectroscopy and electron tunneling. An approximate upper bound on $2\mathrm{\ensuremath{\Delta}}/{T}_{c}$ for conventional superconductors mediated by retarded electron-phonon interactions is proposed.

The momentum-dependent orbital character in crystalline solids, referred to as orbital texture, is of capital importance in the emergence of symmetry-broken collective phases, such as charge density waves as well as superconducting and topological states of matter. By performing extreme ultraviolet multidimensional angle-resolved photoemission spectroscopy for two different crystal orientations linked to each other by mirror symmetry, we isolate and identify the role of orbital texture in photoemission from the transition metal dichalcogenide 1T-TiTe2. By comparing our experimental results with theoretical calculations based on both a quantitative one-step model of photoemission and an intuitive tight-binding model, we unambiguously demonstrate the link between the momentum-dependent orbital orientation and the emergence of strong intrinsic linear dichroism in the photoelectron angular distributions. Our results represent an important step towards going beyond band structure (eigenvalues) mapping and learning about electronic wavefunction and orbital texture of solids by exploiting matrix element effects in photoemission spectroscopy.

We performed angle-resolved photoemission spectroscopy (ARPES) of bulk2H-WSe$_2$ for different crystal orientations linked to each other bytime-reversal symmetry. We introduce a new observable called time-reversaldichroism, which quantifies the modulation of the photoemission intensity uponeffective time-reversal operation. We demonstrate that the hiddenorbital-texture of the crystal's electronic structure leaves its imprint ontothe time-reversal dichroism, due to multiple orbitals interference effects inphotoemission. Our experimental results are in quantitative agreement withstate-of-the-art fully relativistic calculations performed using the one-stepmodel of photoemission. While spin-resolved ARPES probes the spin component ofentangled spin-orbital texture in multiorbital systems, we demonstrate thattime-reversal dichroism is sensitive to its orbital-texture counterpart.

Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern-insulator state and demonstrating clear experimental evidence for its topological nature has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic quantum kinetic calculations including realistic electron-electron and electron-phonon scattering. Our theory provides a direct link to the build up of the Floquet-Chern-insulator state in light-driven graphene and its detection in time- and angle-resolved photoemission spectroscopy (ARPES). This approach allows us to study the robustness of the Floquet features against dephasing and thermalization effects. We also discuss the ultrafast Hall response in the laser-heated state. Furthermore, the induced pseudospin texture and the associated Berry curvature give rise to momentum-dependent orbital magnetization, which is reflected in circular dichroism in ARPES (CD-ARPES). Combining our nonequilibrium calculations with an accurate one-step theory of photoemission allows us to establish a direct link between the build up of the topological state and the dichroic pump-probe photoemission signal. The characteristic features in CD-ARPES are shown to be stable against heating and dephasing effects. Thus, tracing circular dichroism in time-resolved photoemission provides new insights into transient topological properties., M. S. and T. P. D. acknowledge financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. Furthermore, this work is supported by the Swiss National Science Foundation via NCCR MARVEL and the European Research Council via Grant No. ERC-2015-AdG-694097 and ERC Consolidator Grant No. 724103. The Flatiron Institute is a division of the Simons Foundation. M. S. thanks the Alexander von Humboldt Foundation for its support with a Feodor Lynen scholarship and the department. M. A. S. acknowledges financial support from the DFG through the Emmy Noether program (Grant No. SE 2558/2-1).

Orbital polarization and Berry curvature signatures are mapped out by circular dichroism in angle-resolved photoemission., Topologically nontrivial two-dimensional materials hold great promise for next-generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular dichroism angle-resolved photoelectron spectroscopy provides a powerful tool that can resolve the topological and quantum-geometrical character in momentum space. In particular, we investigate how to map out the signatures of the momentum-resolved Berry curvature in two-dimensional materials by exploiting its intimate connection to the orbital polarization. A spin-resolved detection of the photoelectrons allows one to extend the approach to spin-Chern insulators. The present proposal can be extended to address topological properties in materials out of equilibrium in a time-resolved fashion.

We investigate charge pumping in the vicinity of order-obstructed topological phases, i.e. symmetry protected topological phases masked by spontaneous symmetry breaking in the presence of strong correlations. To explore this, we study a prototypical Su-Schrieffer-Heeger model with finite-range interaction that gives rise to orbital charge density wave order, and characterize the impact of this order on the model's topological properties. In the ordered phase, where the many-body topological invariant loses quantization, we find that not only is quantized charge pumping still possible, but it is even assisted by the collective nature of the orbital charge density wave order. Remarkably, we show that the Thouless pump scenario may be used to uncover the underlying topology of order-obstructed phases., 5 pages + supplemental material

Motivated by recent experimental progress we revisit the theory of pump-probe time- and angle-resolved photoemission spectroscopy (trARPES), which is one of the most powerful techniques to trace transient pump-driven modifications of the electronic properties. The pump-induced dynamics can be described in different gauges for the light-matter interaction. Standard minimal coupling leads to the velocity gauge, defined by linear coupling to the vector potential. In the context of tight-binding (TB) models, the Peierls substitution is the commonly employed scheme for single-band models. Multi-orbital extensions -- including the coupling of the dipole moments to the electric field -- have been introduced and tested recently. In this work, we derive the theory of time-resolved photoemission within both gauges from the perspective of nonequilibrium Green's functions. This approach naturally incorporates the photoelectron continuum, which allows for a direct calculation of the observable photocurrent. Following this route we introduce gauge-invariant expressions for the time-resolved photoemission signal. The theory is applied to graphene pumped with short terahertz pulses, which we treat within a first-principles TB model. We investigate the gauge invariance and discuss typical effects observed in subcycle time-resolved photoemission. Our formalism is an ideal starting point for realistic trARPES simulations including scattering effects., Comment: 12 pages, 7 figures; update reference list

Patients are becoming increasingly more independent and self-determined, in addition to having shorter post-operative hospitalization. This is why it is more important than ever to actively involve patients in the follow-up treatment. The question arises as to whether post-operative rehabilitation can be improved with modern devices.As part of a prospective study, the post-operative mobilization was recorded and analyzed by Fitbit®-activity-trackers between 05/2016 and 08/2017 in 100 patients who received a THA. 50 men (Ø 70.6y) and 50 women (Ø 71.1y) were included. Furthermore, the patients were interviewed about their acceptance of the Fitbit®-wristband.The average hospital stay was 7.98 days (SD ± 1.76). The number of steps on the first post-operative day was 712 (SD ± 617). On average (during total hospitalization), 1528 (SD ± 1076) steps were completed daily. One day before discharge, the average number of steps was 2165 (SD ± 1570) on that particular day. There were no gender differences in age and pre-operative Harris hip scores (♂55.3 vs. ♀53.9). Also, there were no statistically significant differences in the number of steps on the first postoperative day (♂745 vs. ♀678). A statistically significant result can be found in the number of steps prior to discharge: on this day, the men took 2483 and the women 1846 steps (p = 0.04). 42% of our patients own a modern smartphone and are able to operate software applications. 52% of the patients found the activity tracker to be motivating, 65% were open to new technologies (e.g. activity trackers) in the hospital. 14% did not check at all or only queried their wristband data once a day, 65% queried 2-4 times/day, and 21% retrieved the data5 times/day.On average, 1528 steps were completed daily. In a comparison of the men and women, the men were only able to demonstrate significantly more steps than the women on the day prior to discharge. The men had significantly shorter hospital stays than the women. The younger the patients, the more mobile they were. A majority of patients are familiar with and/or interested in new technologies. This interest and curiosity should be consciously used for integration in the post-operative treatment.

Staring from the kicked rotator as a paradigm for a system exhibiting classical chaos, we discuss the role of quantum coherence resulting in dynamical localization in the kicked quantum rotator. In this context, the disorder-induced Anderson localization is also discussed. Localization in interacting, quantum many-body systems (many-body localization) may also occur in the absence of disorder, and a practical way to identify its occurrence is demonstrated for an interacting spin chain., Comment: to appear in Acta Physica Polonica A. arXiv admin note: text overlap with arXiv:1708.03169

We study the time evolution of excitonic states after photo-excitation in the one-dimensional spin-less extended Falicov-Kimball model. Several numerical methods are employed and benchmarked against each other: time-dependent mean-field simulations, the second-Born approximation (2BA) within the Kadanoff-Baym formalism, the generalized Kadanoff-Baym Ansatz (GKBA) implemented with the 2BA and the infinite time-evolving block decimation (iTEBD) method. It is found that the GKBA gives the best agreement with iTEBD and captures the relevant physics. We find that excitations to the particle-hole continuum and resonant excitations of the equilibrium exciton result in a qualitatively different dynamics. In the former case, the exciton binding energy remains positive and the frequency of the corresponding coherent oscillations is smaller than the band gap. On the other hand, resonant excitations trigger a collective mode whose frequency is larger than the band gap. We discuss the origin of these different behaviors by evaluating the nonequilibrium susceptibility using the nonthermal distribution and a random phase approximation. The peculiar mode with frequency larger than the band gap is associated with a partial population inversion with a sharp energy cutoff. We also discuss the effects of the cooling by a phonon bath. We demonstrate the real-time development of coherence in the polarization, which indicates excitonic condensation out of equilibrium., Comment: 19 pages, 15 figures

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

We study the coherent non-equilibrium dynamics of interacting two-dimensional systems after a quench from a trivial to a topological Chern insulator phase. While the many-body wavefunction is constrained to remain topologically trivial under local unitary evolution, we find that the Hall response of the system can dynamically approach a thermal value of the post-quench Hamiltonian, even though the efficiency of this thermalization process is shown to strongly depend on the microscopic form of the interactions. Quite remarkably, the effective temperature of the steady state Hall response can be arbitrarily tuned with the quench parameters. Our findings suggest a new way of inducing and observing low temperature topological phenomena in interacting ultracold atomic gases, where the considered quench scenario can be realized in current experimental set-ups., 8 pages, 8 figures (including supplemental material)

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump-probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green's functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract physically relevant information for the interpretation of experiments. We present the open-source software package NESSi (The Non-Equilibrium Systems Simulation package) which allows to perform many-body dynamics simulations based on Green's functions on the L-shaped Kadanoff-Baym contour. NESSi contains the library libcntr which implements tools for basic operations on these nonequilibrium Green's functions, for constructing Feynman diagrams, and for the solution of integral and integro-differential equations involving contour Green's functions. The library employs a discretization of the Kadanoff-Baym contour into time $N$ points and a high-order implementation of integration routines. The total integrated error scales up to $\mathcal{O}(N^{-7})$, which is important since the numerical effort increases at least cubically with the simulation time. A distributed-memory parallelization over reciprocal space allows large-scale simulations of lattice systems. We provide a collection of example programs ranging from dynamics in simple two-level systems to problems relevant in contemporary condensed matter physics, including Hubbard clusters and Hubbard or Holstein lattice models. The libcntr library is the basis of a follow-up software package for nonequilibrium dynamical mean-field theory calculations based on strong-coupling perturbative impurity solvers., Comment: 86 pages, 15 figures

We present results for many-body perturbation theory for the one-body Green's function at finite temperatures using the Matsubara formalism. Our method relies on the accurate representation of the single-particle states in standard Gaussian basis sets, allowing to efficiently compute, among other observables, quasiparticle energies and Dyson orbitals of atoms and molecules. In particular, we challenge the second-order treatment of the Coulomb interaction by benchmarking its accuracy for a well-established test set of small molecules, which includes also systems where the usual Hartree-Fock treatment encounters difficulties. We discuss different schemes how to extract quasiparticle properties and assess their range of applicability. With an accurate solution and compact representation, our method is an ideal starting point to study electron dynamics in time-resolved experiments by the propagation of the Kadanoff-Baym equations., 12 pages, 8 figures

The nonequilibrium Green's functions (NEGF) approach is a versatile theoretical tool, which allows to describe the electronic structure, spectroscopy, and dynamics of strongly correlated systems. The applicability of this method is, however, limited by its considerable computational cost. Due to the treatment of the full two-time dependence of the NEGF, the underlying equations of motion involve a long-lasting non-Markovian memory kernel that results in at least an N3t scaling in the number of time points Nt. The system's memory time is, however, reduced in the presence of a thermalizing bath. In particular, dynamical mean field theory (DMFT), one of the most successful approaches to strongly correlated lattice systems, maps extended systems to an effective impurity coupled to a bath. In this work, we systematically investigate how the memory time can be truncated in nonequilibrium DMFT simulations of the Hubbard and Hubbard-Holstein models. We show that suitable truncation schemes, which substantially reduce the computational cost, result in excellent approximations to the full time evolution. This approach enables the propagation to longer times, making fundamental processes such as prethermalization and the final stages of thermalization accessible to nonequilibrium DMFT.

We investigate the laser-induced dynamics of electronically driven charge-density-wave order. A comprehensive mean-field analysis of the attractive Hubbard model in the weak-coupling regime reveals ultrafast switching and ultrafast melting of the order via a nonthermal pathway. The resulting nonequilibrium phase diagram exhibits multiple dynamical phase transitions with increasing field strength. Using an intuitive pseudospin picture, we show that the laser can be regarded as a external (pseudo) magnetic field, and that the distinct dynamical regimes can be connected to the spin precession angle. We furthermore study the effects of electron-electron interactions beyond mean-field to show that the main features of the phase diagram are robust against scattering or thermalization processes. For example, the nonthermal state with switched order is characterized by a particularly slow relaxation. We also demonstrate how these nonthermal phases can be stabilized by tailoring the pulse shape with optimal control theory., 5 + 7 pages

Many-body localization (MBL) is an emergent phase in correlated quantum systems with promis- ing applications, particularly in quantum information. Here, we unveil the existence and analyse this phase in a chiral multiferroic model system. Conventionally, MBL occurrence is traced via level statistics by implementing a standard finite-size scaling procedure. Here, we present an approach based on the full distribution of the ratio of adjacent energy spacings. We find a strong broadening of the histograms of counts of these level spacings directly at the transition point from MBL to the ergodic phase. The broadening signals reliably the transition point without relying on an averaging procedure. The fast convergence of the histograms even for relatively small systems allows moni- toring the MBL dynamics with much less computational effort. Numerical results are presented for a chiral spin chain with a dynamical Dzyaloshinskii Moriya (DM) interaction, an established model to describe the spin excitations in a single phase spin-driven multiferroic system. The multiferroic MBL phase is uncovered and it is shown how to steer it via electric fields., Comment: 8 pages, 10 figures, keywords: MBL, disorder, fluctuation, multiferroic, transition, GOE, GUE

This study demonstrates how the spin quantum dynamics of a single Fe atom adsorbed on Cu(001) can be controlled and manipulated by the vibrations of a nearby copper tip attached to a nano cantilever by virtue of the dynamic magnetic anisotropy. The magnetic properties of the composite system are obtained from \emph{ab initio} calculations in completely relaxed geometries and turned out to be dependent considerably on the tip-iron distance that changes as the vibrations set in. The level populations, the spin dynamics interrelation with the driving frequency, as well as quantum information related quantities are exposed and analyzed., accepted in New Journal of Physics

In this paper we study the time evolution of the entanglement between two remote NV Centers (nitrogen vacancy in diamond) connected by a dual-mode nanomechanical resonator with magnetic tips on both sides. Calculating the negativity as a measure for the entanglement, we find that the entanglement between two spins oscillates with time and can be manipulated by varying the parameters of the system. We observed the phe- nomenon of a sudden death and the periodic revivals of entanglement in time. For the study of quantum deco- herence, we implement a Lindblad master equation. In spite of its complexity, the model is analytically solvable under fairly reasonable assumptions, and shows that the decoherence influences the entanglement, the sudden death, and the revivals in time., to appear in J.Phys. B

Chern insulators exhibit fascinating properties which originate from the topologically nontrivial state characterized by the Chern number. How these properties change if the system is quenched between topologically distinct phases has however not been systematically explored. In this work, we investigate the quench dynamics of the prototypical massive Dirac model for topological insu- lators in two dimensions. We consider both dissipation-less dynamics and the effect of electron- phonon interactions, and ask how the transient dynamics and nonequilibrium steady states affect simple observables. Specifically, we discuss a time-dependent generalization of the Hall effect and the dichroism of the photoexcitation probability between left and right circularly polarized light. We present optimized schemes based on these observables, which can reveal the evolution of the topological state of the quenched system., Comment: 15 pages, 14 figures

Die Themen Suizidalitat und die suizidale Gefahrdung bestimmter Risikogruppen unserer Gesellschaft, z. B. von psychisch kranken Menschen, von alteren und alten Menschen, von Menschen in existenziell bedrohlichen Krisen, werden erst in den letzten Jahrzehnten vermehrt zur Kenntnis genommen. Suizidpravention im Alter steht sehr schnell im ethischen Spannungsfeld zwischen Anspruch auf Hilfe, wo es um Unterstutzung bei Erkrankung und psychosozialer Situation geht, und arztlicher Fursorgepflicht. Anderseits findet man sich rasch in einer „Grauzone von stillschweigender Toleranz“ angesichts der sog. demografischen Uberalterung der Gesellschaft mit ihren realen und auch vermeintlichen Folgeproblemen fur den Einzelnen und die Solidargemeinschaft sowie angesichts der Rationalisierungs- und Rationierungsdebatte im Gesundheitswesen, bei der alte Menschen unter Kosten-Nutzen-Kautelen den Kurzeren ziehen konnten (Erlemeier 2001).

A quantum thermodynamic cycle with a chiral multiferroic working substance such as $\textrm{LiCu}_{2}\textrm{O}_{2}$ is presented. Shortcuts to adiabaticity are employed to achieve an efficient, finite time quantum thermodynamic cycle which is found to depend on the spin ordering. The emergent electric polarization associated with the chiral spin order, i.e. the magnetoelectric coupling, renders possible steering of the spin order by an external electric field and hence renders possible an electric-field control of the cycle. Due to the intrinsic coupling between of the spin and the electric polarization, the cycle performs an electro-magnetic work. We determine this work's mean square fluctuations, the irreversible work, and the output power of the cycle. We observe that the work mean square fluctuations are increased with the duration of the adiabatic strokes while the irreversible work and the output power of the cycle show a non-monotonic behavior. In particular the irreversible work vanishes at the end of the quantum adiabatic strokes. This fact confirms that the cycle is reversible. Our theoretical findings evidence the existence of a system inherent maximal output power. By implementing a Lindblad master equation we quantify the role of thermal relaxations on the cycle efficiency. We also discuss the role of entanglement encoded in the non-collinear spin order as a resource to affect the quantum thermodynamic cycle., Comment: 13pages, 15 figures, submitted in Phys. Rev. E

Experiment and theory evidence a new pathway for correlated two-electron release from many-body compounds following collective excitation by a single photon. Using nonequilibrium Green’s function approach we trace plasmon oscillations as the key ingredient of the effective electron-electron interaction that governs the correlated pair emission in a dynamic many-body environment. Results from a full ab initio implementation for C60 fullerene are in line with experimental observations. The findings endorse the correlated two-electron photoemission as a powerful tool to access electronic correlation in complex systems.

New journal of physics 18(11), 113055 (2016). doi:10.1088/1367-2630/18/11/113055, Fullerene complexes may play a key role in the design of future molecular electronics and nanostructured devices with potential applications in light harvesting using organic solar cells. Charge and energy flow in these systems is mediated by many-body effects. We studied the structure and dynamics of laser-induced multi-electron excitations in isolated C60 by two-photon photoionization as a function of excitation wavelength using a tunable fs UV laser and developed a corresponding theoretical framework on the basis of ab initio calculations. The measured resonance line width gives direct information on the excited state lifetime. From the spectral deconvolution we derive a lower limit for purely electronic relaxation on the order of ${\tau }_{\mathrm{el}}={10}_{-3}^{+5}$ fs. Energy dissipation towards nuclear degrees of freedom is studied with time-resolved techniques. The evaluation of the nonlinear autocorrelation trace gives a characteristic time constant of ${\tau }_{\mathrm{vib}}=400\pm 100$ fs for the exponential decay. In line with the experiment, the observed transient dynamics is explained theoretically by nonadiabatic (vibronic) couplings involving the correlated electronic, the nuclear degrees of freedom (accounting for the Herzberg–Teller coupling), and their interplay., Published by Dt. Physikalische Ges., [Bad Honnef]

Psychiatrie und Psychotherapie sind Facher mit einem hohen Anteil ethischer Fragestellungen. Das Thema Selbstbestimmung steht derzeit vollig im Vordergrund. Die ethischen „corner stones“ Autonomie, Gutes tun, Nicht schaden und Gerechtigkeit werden diskutiert.

This work provides a unified theoretical treatment of the single- and correlated double-electron emission from a general electronic system. Using Feshbach projection method, the states of interest are selected by the projection operator; the Feshbach-Schur map determines the effective Hamiltonian and the optical potential for the emitted electrons. On the other hand, the nonequilibrium Green's functions method is demonstrated to be a complementary approach, and an explicit correspondence between both methods is established. For a self-contained exposition, some results on single-electron emission are rederived using both formalisms. New insights and results are obtained for the correlated electron-pair emission: This includes the effective two-electron Hamiltonian, the explicit form of the Feshbach self-energy in terms of the many-body self-energies, and the diagrammatic expansion of the two-particle current. As an illustration of the diagrammatic technique, the process of the two-particle emission assisted by the excitation of plasmons is explicitly worked out.