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1. Ultrafast Evolution of Bulk, Surface and Surface Resonance States in Photoexcited Bi$_{2}$Te$_{3}$

Author

Hedayat, Hamoon, Bugini, Davide, Yi, Hemian, Chen, Chaoyu, Zhou, Xingjiang, Cerullo, Giulio, Dallera, Claudia, and Carpene, Ettore

Subjects
Physics - Applied Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

We use circular dichroism (CD) in time- and angle-resolved photoemission spectroscopy (trARPES) to measure the femtosecond charge dynamics in the topological insulator (TI) Bi$_{2}$Te$_{3}$. We detect clear CD signatures from topological surface states (TSS) and surface resonance (SR) states. In time-resolved measurements, independently from the pump polarization or intensity, the CD shows a dynamics which provides access to the unexplored electronic evolution in unoccupied states of Bi$_{2}$Te$_{3}$. In particular, we are able to disentangle the unpolarized electron dynamics in the bulk states from the spin-textured TSS and SR states on the femtosecond timescale. Our study demonstrates that photoexcitation mainly involves the bulk states and is followed by sub-picosecond transport to the surface. This provides essential details on intra- and interband scatterings in the relaxation process of TSS and SR states. Our results reveal the significant role of SRs in the subtle ultrafast interaction between bulk and surface states in TIs.

Published
2021
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2. Investigation of the Non-equilibrium State of Strongly Correlated Materials by Complementary Ultrafast Spectroscopy Techniques

Author

Hedayat, Hamoon, Sayers, Charles J., Ceraso, Arianna, van Wezel, Jasper, Clark, Stephen R., Dallera, Claudia, Cerullo, Giulio, Da Como, Enrico, and Carpene, Ettore

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Photoinduced non-thermal phase transitions are new paradigms of exotic non-equilibrium physics of strongly correlated materials. An ultrashort optical pulse can drive the system to a new order through complex microscopic interactions that do not occur in the equilibrium state. Ultrafast spectroscopies are unique tools to reveal the underlying mechanisms of such transitions which lead to transient phases of matter. Yet, their individual specificities often do not provide an exhaustive picture of the physical problem. One effective solution to enhance their performance is the integration of different ultrafast techniques. This provides an opportunity to simultaneously probe physical phenomena from different perspectives whilst maintaining the same experimental conditions. In this context, we performed complementary experiments by combining time-resolved reflectivity and time and angle-resolved photoemission spectroscopy. We demonstrated the advantage of this combined approach by investigating the complex charge density wave (CDW) phase in 1$\it{T}$-TiSe$_{2}$. Specifically, we show the key role of lattice degrees of freedom to establish and stabilize the CDW in this material.

Published
2020
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3. Excitonic and lattice contributions to the charge density wave in 1T-TiSe$_2$ revealed by a phonon bottleneck

Author

Hedayat, Hamoon, Sayers, Charles J., Bugini, Davide, Dallera, Claudia, Wolverson, Daniel, Batten, Tim, Karbassi, Sara, Friedemann, Sven, Cerullo, Giulio, van Wezel, Jasper, Clark, Stephen R., Carpene, Ettore, and Da Como, Enrico

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Understanding collective electronic states such as superconductivity and charge density waves is pivotal for fundamental science and applications. The layered transition metal dichalcogenide 1T-TiSe2 hosts a unique charge density wave (CDW) phase transition whose origins are still not fully understood. Here, we present ultrafast time- and angle-resolved photoemission spectroscopy (TR-ARPES) measurements complemented by time-resolved reflectivity (TRR) which allows us to establish the contribution of excitonic and electron-phonon interactions to the CDW. We monitor the energy shift of the valence band (VB) and coupling to coherent phonons as a function of laser fluence. The VB shift, directly related to the CDW gap closure, exhibits a markedly slower recovery dynamics at fluences above Fth = 60 microJ cm-2. This observation coincides with a shift in the relative weight of coherently coupled phonons to higher frequency modes in time-resolved reflectivity (TRR), suggesting a phonon bottleneck. Using a rate equation model, the emergence of a high-fluence bottleneck is attributed to an abrupt reduction in coupled phonon damping and an increase in exciton dissociation rate linked to the loss of CDW superlattice phonons. Thus, our work establishes the important role of both excitonic and phononic interactions in the CDW phase transition and the advantage of combining complementary femtosecond techniques to understand the complex interactions in quantum materials., Comment: 11 pages, 4 figures

Published
2019
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7. Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa2Cu3O7 Films

Author

Moretti Sala, Marco, primary, Salluzzo, Marco, additional, Minola, Matteo, additional, De Luca, Gabriella Maria, additional, Dellea, Greta, additional, Srot, Vesna, additional, Wang, Yi, additional, van Aken, Peter A., additional, Le Tacon, Matthieu, additional, Keimer, Bernhard, additional, Dallera, Claudia, additional, Braicovich, Lucio, additional, and Ghiringhelli, Giacomo, additional

Published
2020
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8. Ultrafast surface state dynamics of topological insulators metamaterials at optical frequencies

Author

Hedayat, Hamoon, Vezzoli, Stefano, Sun, Xinxing, Krishnamoorthy, Harish N.S., Cerullo, G., Dallera, Claudia, Carpene, Ettore, Zheludev, Nikolai, Adamo, Giorgio, and Soci, Cesare

Subjects
topological insulator, metamaterials, ultrafast, Condensed Matter::Superconductivity, Physics::Optics, Condensed Matter::Strongly Correlated Electrons
Abstract

We report time-resolved pump-probe and ARPES measurements of topological insulator crystals and nanoslit metamaterials of BixSb1-xTeySe1-y (BSTS) at optical frequencies, which reveal the ultrafast dynamics of topological surface states at room temperature.

Published
2019

13. Advanced spectroscopies of graphene and 2D materials

Author

Pietralunga, Silvia Maria, primary, Manzoni, Cristian, additional, Carpene, Ettore, additional, Bugini, Davide, additional, Dal Conte, Stefano, additional, Hedayat, Hamoon, additional, Soavi, Giancarlo, additional, Vahid, Mohammad J., additional, Virgili, Tersilla, additional, Zani, Maurizio, additional, Dallera, Claudia, additional, Sordan, Roman, additional, Tagliaferri, Alberto, additional, and Cerullo, Giulio, additional

Published
2016
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14. Nonpareil Yb Behavior in YbMn 6 Ge 6-x Sn x

Author

Mazet, Thomas, Malterre, Daniel, François, Michel, Dallera, Claudia, Grioni, G, Monaco, G, Institut Jean Lamour (IJL), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), INFM-Dipartimento di Fisica-Politecnico di Milano, Istituto Nazionale di Fisica Nucleare (INFN), Institute of Condensed Matter Physics [Lausanne], Ecole Polytechnique Fédérale de Lausanne (EPFL), and European Synchrotron Radiation Facility (ESRF)

Subjects
[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat], [CHIM.INOR]Chemical Sciences/Inorganic chemistry, PACS: 71.20.Lp, 65.40.De, 71.10.-w, 71.27.+a
Abstract

Équipe 102 : Surfaces et Spectroscopies ; Équipe 103 : Composés intermétalliques et matériaux hybrides; International audience; We investigate the temperature dependence of the Yb valence in YbMn 6 Ge 1:8 Sn 4:2 and YbMn 6 Ge 1:6 Sn 4:4 using resonant inelastic x-ray scattering experiments. Yb is found to be in an intermediate valent state in the whole investigated temperature range (10–450 K). We thus prove that the unusually high magnetic ordering temperature of Yb ( 60 and 90 K for x ¼ 4:2 and 4.4, respectively) involves an intermediate valent Yb, an unprecedentedly observed phenomenon. Further, an anomalous increase in the Yb valence is observed upon cooling. A scenario is proposed to explain this unusual behavior. It is based on the presence of magnetically ordered Mn moments and on an Anderson Hamiltonian with a Zeeman term modeling the magnetic interactions.

Published
2013
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16. Observation of Two Nondispersive Magnetic Excitations in NiO by Resonant Inelastic Soft-X-Ray Scattering

Author

Ghiringhelli, GIACOMO CLAUDIO, Piazzalunga, Andrea, Dallera, Claudia, Braicovich, Lucio, Schmitt, T., Strocov, V. N., Schlappa, J., Patthey, L., Wang, X., Berger, H., and Grioni, Marco

Subjects
Physics, Condensed matter physics, Magnetic moment, Wave Dispersion, Scattering, General Physics and Astronomy, Inelastic scattering, Spectral line, Inelastic neutron scattering, Resonant inelastic X-ray scattering, symbols.namesake, X-ray Raman scattering, symbols, Atomic physics, Optical-Absorption, Raman-Scattering, Raman scattering
Abstract

We present high resolution (DeltaE=120 meV) resonant inelastic x-ray scattering data measured at the Ni L3 edge (2p_{3/2}--3d) on the paradigmatic antiferromagnetic oxide NiO. Spectra reveal clear signatures of magnetic excitations at approximately 95 and approximately 190 meV whose energy seems independent from transferred momentum. These spectral features are well reproduced by a single Ni2+ ion model in an effective exchange field. Within this local model the two magnetic excitations are characterized by a variation of the atomic magnetic moment along the local ordering direction (DeltaS_{alpha}) of one and two units. The DeltaS_{alpha}=2 case has different nature from bimagnons observed in optical Raman spectra, for which DeltaS_{alpha}=0.

Published
2009
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17. Combining M- and L-edge resonant inelastic x-ray scattering for studies of 3d transition metal compounds

Author

Chiuzbaian, S. G., Schmitt, T., Matsubara, M., Kotani, A., Ghiringhelli, GIACOMO CLAUDIO, Dallera, Claudia, Tagliaferri, Alberto, Braicovich, Lucio, Scagnoli, V., Brookes, N. B., Staub, U., and Patthey, L.

Subjects
Condensed Matter::Strongly Correlated Electrons, 2ND-HARMONIC GENERATION, D-D EXCITATIONS, EMISSION-SPECTROSCOPY, COO, ABSORPTION-SPECTRA
Abstract

Resonant inelastic x-ray scattering (RIXS) measurements performed jointly across the M-2,M-3 and L-3 absorption thresholds are used to study CoO local electronic structure and are supported by model calculations. The high-resolution experimental data provide a precise set of parameters to describe the correlated response of valence electrons. The same core-hole independent set of parameters within the single impurity Anderson model is used to describe both the M (3p-3d) and L (2p-3d) resonances. This work shows that combining M and L scattering data provides an enhanced contrast view of the spectral weights. Measured M-2,M-3-RIXS spectra are observed to be free of charge-transfer or normal fluorescence contributions. Moreover the cross section of M-RIXS final states with change in spin multiplicity is low. Combining this information with L-edge studies establishes an appealing means of making a better separation between on-site and intersite (ligand to metal) electronic excitations. Experimental and theoretical features specific to RIXS studies performed at M and L edges are summarized as a basis for future studies on complex transition metal compounds.

Published
2008

39. Angle Resolved Photoemission from Nd(1.85)Ce(0.15)CuO(4) using High Energy Photons : A Fermi Surface Investigation

Author

Claesson, Thomas, Månsson, Martin, Dallera, Claudia, Venturini, Federica, De Nadaï, Celine, Brookes, Nicholas B., Tjernberg, Oscar, Claesson, Thomas, Månsson, Martin, Dallera, Claudia, Venturini, Federica, De Nadaï, Celine, Brookes, Nicholas B., and Tjernberg, Oscar

Abstract

We have performed an angle resolved photoemission study on a single crystal of the optimally electron doped (n-type) cuprate superconductor Nd2-xCexCuO4 (x=0.15) at a photon energy of 400 eV. The Fermi surface is mapped out and is, in agreement with earlier measurements, of hole-type with the expected Luttinger volume. However, comparing with previous low energy measurements, we observe a different Fermi surface shape and a different distribution of spectral intensity around the Fermi surface contour. The observed Fermi surface shape indicates a stronger electron correlation in the bulk as compared to the surface., QC 20100702 QC 20110916

Published
2004
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43. Kondo Lattice Effects of YbAl3Suggested by Temperature Dependence of High-Accuracy High-Energy Photoelectron Spectroscopy

Author

Suga, Shigemasa, primary, Sekiyama, Akira, additional, Imada, Shin, additional, Shigemoto, Akihiko, additional, Yamasaki, Atsushi, additional, Tsunekawa, Masanori, additional, Dallera, Claudia, additional, Braicovich, Lucio, additional, Lee, Tien-Lin, additional, Sakai, Osamu, additional, Ebihara, Takao, additional, and Ōnuki, Yoshichika, additional

Published
2005
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48. Charge disproportionation in RNiO3 perovskites (R=rare earth) from high-resolution x-ray absorption spectroscopy

Author

Medarde, M., Dallera, Claudia, Grioni, M., Delley, B., Vernay, F., Mesot, J., Sikora, M., Alonso, J. A., and Martínez Lope, M. J.

Subjects
Rare-Earth, Ynio3, Metal-Insulator-Transition, Spectra, praseodymium compounds, Electronic-Structure, X-ray absorption spectra, rare earth compounds, Manganites, lutetium compounds, metal-insulator transition, Superconductors, Mn K-Edge, State
Abstract

High-resolution x-ray absorption measurements reveal a rare-earth-dependent splitting of the Ni K edge in the insulating, charge-disproportionated state of the whole RNiO3 perovskite family. The splitting is five times larger for LuNiO3 [2.5(1) eV] than for PrNiO3 [0.5(3) eV], suggesting that the charge transfer between Ni3+delta and Ni3-delta decreases by approaching the itinerant limit and is larger for the heavier lanthanides than suggested in previous studies. The spectroscopic signature of the two Ni sites remains visible above the metal-insulator transition, in agreement with the persistence of dynamic Ni3+delta/Ni3-delta charge fluctuations in the metallic phase. This last result generalizes the occurrence of charge disproportionation as alternative to Jahn-Teller distortions to the dynamic regime, giving further support to recent theoretical work [I. I. Mazin, D. I. Khomskii, R. Lengsdorf, J. A. Alonso, W. G. Marshall, R. M. Ibberson, A. Podlesnyak, M. J. Martiacutenez-Lope, and M. M. Abd-Elmeguid, Phys. Rev. Lett. 98, 176406 (2007)].

49. alpha-gamma transition in metallic Ce studied by resonant x-ray spectroscopies

Author

Dallera, Claudia, Grioni, M., Palenzona, A., Taguchi, M., Annese, E., Ghiringhelli, GIACOMO CLAUDIO, Tagliaferri, Alberto, Brookes, N. B., Neisius, T. H., and Braicovich, Lucio

Subjects
Polarization Dependence, Scattering, Ground-State, Systems, State Properties, Cerium, Spectra, Electronic-Structure, Photoemission, Emission-Spectroscopy
Abstract

We performed bulk-sensitive x-ray absorption (XAS) in the partial fluorescence yield (PFY) mode, and resonant x-ray emission (RXES) measurements of the solid solution Sc (7 at.%):Ce at the Ce L-3 (2p-->5d) and M-4,M-5 (3d-->4f) absorption edges. We deduce an increasing 4f-band hybridization from the gamma-phase stable at room temperature to the low-temperature alpha-Ce, consistent with the "Kondo collapse" scenario for the transition. The enhanced intrinsic resolution of PFY-XAS allows us to resolve the elusive three-peak structure predicted by theory. Thanks to the selective enhancement typical of RXES, we could estimate the small but non-negligible contribution of the f(2) configuration in the hybrid ground state, and its change in the two phases. The linear dichroism effect in the M-4,M-5 RXES spectra is consistent with the observed hybridization of 4f and conduction states.

50. Revealing the charge density in solids

Author

Månsson, Martin, Claesson, Thomas, Finazzi, Marco, Dallera, Claudia, De Nadaï, Celine, Brookes, Nicholas B., Tjernberg, Oscar, Månsson, Martin, Claesson, Thomas, Finazzi, Marco, Dallera, Claudia, De Nadaï, Celine, Brookes, Nicholas B., and Tjernberg, Oscar

Abstract

QC 20100702

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