X-ray study of femtosecond structural dynamics in the 2D charge density wave compound 1T-TaS2

Laulhé, Claire; Cario, Laurent; Corraze, B.; Janod, Étienne; Huber, Tim; Lantz, Gabriel; Boulfaat, S.; Ferrer, Amparo González; Mariager, S. O.; Johnson, Jeremy A.; Grübel, S.; Lübcke, A.; Ingold, G.; Beaud, P.; Johnson, Steven L.; Ravy, S.

doi:10.1016/j.physb.2014.11.049

Cited by 14 publications

(16 citation statements)

References 26 publications

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“…In fact, the recovery occurs slower than any other process observed in our experiment which implies that either non-local relaxation phenomena (mapped via k-dependent studies not performed here) or non-thermalized states in the lattice system are responsible for the slow re-equilibration of the electronic subsystem. In fact, such long-living non-equilibrium situations in the lattice system have been reported earlier [35] and are also present here.…”

Section: Experiments and Resultssupporting

confidence: 84%

“…A particular finding is that the recovery of this non-equilibrium state is only partial, as the LHB intensity is not fully restored after several ps. Similar persisting, transient states were also observed during the structural response of photo-excited 1T-TaS 2 [35], where the formation of a long-living (>10 ps), quasi-equilibrated lattice state was found to occur on timescales comparable to the LHB recovery times discussed here. Our data clearly show a link between the CDW periodic lattice distortion and short-range electronic correlations, as both signatures show the same saturating behavior, see Figures 3a and 4b.…”

Section: Discussionsupporting

confidence: 78%

“…(iii) The LHB signature recovers due to the reformation of the Mott state on the 1 ps time scale. The final, quasi-equilibrated state after a few ps is different from the initial state as evident from partial recovery of LHB intensity (Figure 3b) and characterized by an decreased amplitude of the CDW lattice distortion [35] that persists up to the time scale of 10 ps, where the CDW amplitude mode phonon is largely damped out due to anharmonic coupling.…”

Section: Discussionmentioning

confidence: 95%

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Excitation and Relaxation Dynamics of the Photo-Perturbed Correlated Electron System 1T-TaS2

et al. 2018

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We investigate the perturbation and subsequent recovery of the correlated electronic ground state of the Mott insulator 1T-TaS 2 by means of femtosecond time-resolved photoemission spectroscopy in normal emission geometry. Upon an increase of near-infrared excitation strength, a considerable collapse of the occupied Hubbard band is observed, which reflects a quench of short-range correlations. It is furthermore found that these excitations are directly linked to the lifting of the periodic lattice distortion which provides the localization centers for the formation of the insulating Mott state. We discuss the observed dynamics in a localized real-space picture.

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Section: Experiments and Resultssupporting

confidence: 84%

Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 95%

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Excitation and Relaxation Dynamics of the Photo-Perturbed Correlated Electron System 1T-TaS2

et al. 2018

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“…Below 180 K, these discommensuration regions disappear and the material becomes insulating, forming the commensurate (C) phase. Femtosecond laser excitation has been shown to trigger transitions from the C and NC phases to the NC and I phases, respectively [8,9]. The photoinduced NC to I transition is the focus of the present work.…”

Section: Introductionmentioning

confidence: 95%

Domain-size effects on the dynamics of a charge density wave in 1T−TaS2

et al. 2017

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Recent experiments have shown that the high temperature incommensurate (I) charge density wave (CDW) phase of 1T-TaS2 can be photoinduced from the lower temperature, nearly commensurate (NC) CDW state. Here we report a time-resolved x-ray diffraction study of the growth process of the photoinduced I-CDW domains. The layered nature of the material results in a marked anisotropy in the size of the photoinduced domains of the I-phase. These are found to grow self-similarly, their shape remaining unchanged throughout the growth process. The photoinduced dynamics of the newly formed I-CDW phase was probed at various stages of the growth process using a double pump scheme, where a first pump creates I-CDW domains and a second pump excites the newly formed I-CDW state. We observe larger magnitudes of the coherently excited I-CDW amplitude mode in smaller domains, which suggests that the incommensurate lattice distortion is less stable for smaller domain sizes.

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“…Diffraction techniques are especially well adapted to study CDW compounds [5,10,12,14,15,22,[24][25][26][27][28][29]. Indeed, a structural modulation with wavevector q gives rise to satellite peaks located at positions ± q with respect to each regular lattice peak (Fig.…”

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confidence: 99%

Ultrafast Formation of a Charge Density Wave State in 1T−TaS2 : Observation at Nanometer Scales Using Time-Resolved X-Ray Diffraction

et al. 2017

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Femtosecond time-resolved X-ray diffraction is used to study a photo-induced phase transition between two charge density wave (CDW) states in 1T-TaS2, namely the nearly commensurate (NC) and the incommensurate (I) CDW states. Structural modulations associated with the NC-CDW order are found to disappear within 400 fs. The photo-induced I-CDW phase then develops through a nucleation/growth process which ends 100 ps after laser excitation. We demonstrate that the newly formed I-CDW phase is fragmented into several nanometric domains that are growing through a coarsening process. The coarsening dynamics is found to follow the universal Lifshitz-Allen-Cahn growth law, which describes the ordering kinetics in systems exhibiting a non-conservative order parameter.Among strongly correlated electron systems, superconductors and materials exhibiting metal-insulator transitions are usually characterized by strong electronelectron and electron-phonon couplings [1][2][3]. At thermodynamic equilibrium, the corresponding many-body interactions lead to rich phase diagrams as a function of temperature, pressure or doping. Such compounds also display fascinating out-of-equilibrium physics, in the form of ultra-fast symmetry changes known as photoinduced phase transitions [4][5][6], and occurrence of new, transient states [6][7][8].Charge density wave (CDW) states are broken symmetry states of metals arising from electron-phonon interactions. They are characterized by a periodic modulation of both atomic positions and electron density. The metal-to-CDW phase transition is characterized by the growth of a complex-valued order parameter p = A exp iΦ , which reflects both the amplitude A and the phase Φ of the periodic modulation [3]. A number of photo-induced phase transitions that have been achieved in CDW compounds correspond to a suppression of the CDW order, i.e. a transition between a CDW state and a metallic state free of any structural modulation [5,[9][10][11][12][13][14][15]. Among those, the photo-induced suppression of the CDW state in blue bronze was shown to involve a coherent motion of atoms along the normal coordinates of the CDW amplitude mode [5]. In this case, the amplitude mode allows continuous variations of the modulus of the order parameter |p|, the metallic state corresponding to |p|=0. In the present work, we focus on the photo-induced phase transition between the nearly commensurate (NC) and the incommensurate (I) CDW states in 1T-TaS 2 , which exhibit two distinct order parameters. When thermallyinduced, this first-order phase transition involves a discontinuous change of atomic positions, and a coexistence of NC and I phase domains over a 3 K range [16,17]. It is thus expected that the photo-induced I phase appears through non-coherent atomic motions, by a nucleation/growth process. We report that the photo-induced NC → I phase is completed within 100 ps after laser excitation. At this 100 ps delay, the photo-induced I-CDW phase is found divided into domains with a typical size of 150Å. Its ordering kinet...

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X-ray study of femtosecond structural dynamics in the 2D charge density wave compound 1T-TaS2

Cited by 14 publications

References 26 publications

Excitation and Relaxation Dynamics of the Photo-Perturbed Correlated Electron System 1T-TaS2

Excitation and Relaxation Dynamics of the Photo-Perturbed Correlated Electron System 1T-TaS2

Domain-size effects on the dynamics of a charge density wave in 1T−TaS2

Ultrafast Formation of a Charge Density Wave State in 1T−TaS2 : Observation at Nanometer Scales Using Time-Resolved X-Ray Diffraction

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