Photoinduced interlayer dynamics in Td-MoTe2: A broadband pump-probe study

Abstract

We report on time-resolved broadband transient reflectivity (tr-bb-TR) measurements performed on a bulk single crystal of Td-MoTe2 as a function of the incident pump fluence ( F). Tr-bb-TR data unveil photoinduced electronic changes progressing on the sub-picosecond timescale as well as the dynamics of the coherent low-frequency 1A1 interlayer shear phonon. Our results indicate a gradual evolution of both the TR and the 1A1 Fourier intensity spectra as a function of F, ruling out the threshold-like change that has been associated with the ultrafast photoinduced Td → 1 T ′ phase transition. We also observe a large redshift of the 1A1 Fourier spectral features, which implies that large renormalization effects are taking place on the interband transitions that are dielectrically susceptible to the 1A1 interlayer shear phonon displacement.

Traversing Double-Well Potential Energy Surfaces: Photoinduced Concurrent Intralayer and Interlayer Structural Transitions in XTe2 (X = Mo, W)

“…The discrepancy may derive from the limited optical penetration depth and the identified interlayer stacking faults. In addition, the electron–phonon thermalization (or the Debye–Waller effect) may be another significant energy relaxation pathway, competing with the structural transitions. The twin structures and the stacking faults in both the 1T′ and the Td phases of XTe 2 are identified by the ultrafast structural response (see Figures S3 and S4), which indicates the suppression of the local DWPES corresponding to defects in XTe 2 .…”

“…The discrepancy may derive from the limited optical penetration depth and the identified interlayer stacking faults. In addition, the electron−phonon thermalization (or the Debye−Waller effect) may be another significant energy relaxation pathway, 43 competing with the structural transitions.…”

Persistent Photogenerated State Attained by Femtosecond Laser Irradiation of Thin Td-MoTe2

“…Such breaking of inversion symmetry causes the appearance of a low-frequency Raman-active 1 A 1 ≈ 13 cm –1 interlayer shear mode (Figure b). The latter has been exploited as a parameter to follow the aforementioned first-order thermal phase change ,, as well as possible PIPTs. − …”

Ultrafast transport mediated homogenization of photoexcited electrons governs the softening of the $A_\mathrm{1g}$ phonon in bismuth

“…They enable broad spectral detection and the observation of spectroscopic effects that are not evident when single or two-color fs-TR are employed due to e.g. thin film interference effects or absorption minima and maxima arising from critical points in the dielectric function [26].…”

“…Ultimately the sign flip of ∆R/R 0 in (a) leads to a phase node or nonoscillatory signal in the time domain at λ probe ≈ 650 nm as seen in the corresponding trace for d = 27 nm in (b). This renders any analysis based on the direct comparison of phonon oscillation amplitudes at a single probe wavelength near λ probe ≈ 650 nm very challenging, highlighting the advantages of broadband-over single-color probes [26].…”