Ultrafast terahertz dynamics of the photo-induced structural change in a type-II Weyl semimetal

Predicted to be the first type-II Weyl semimetal, Td-WTe2 has been found to exhibit many novel properties, including giant magnetoresistance, nonlinear anomalous Hall effect and chiral anomaly [1-3]. One fascinating feature is its tendency toward a topological trivial metastable phase as the consequence of a structural symmetry change induced by ultrafast laser pulse [4,5]. To date, there still is a lack of experimental investigation on the electrodynamics of the low-energy quasiparticles in this photo-induced metastable state. In this study, we present findings from ultrafast terahertz dynamic study of a Td-WTe2 thin film, driven into the transient state by intense near-IR laser pulses. Our results show that the terahertz electrodynamics in the photo-induced phase can be well explained by the Drude model, similar to that of the equilibrium state. However, a reduced scattering rate and plasma frequency were observed by comprehensive optical conductivity analysis, excluding thermal effect and suggesting a slight modification to the band dispersion at the Fermi level. Our work provides direct spectroscopic evidence of electronic-band renormalization that is correlated to the photo-induced structural transition in Td-WTe2.

[1] M. N. Ali et al., Nature 514, 205 (2014).

[2] K. Kang et al., Nature materials 18, 324 (2019).

[3] R. Adhikari et al., Nanomaterials 11, 2755 (2021).

[4] S. Ji, O. Granas, and J. Weissenrieder, ACS nano 15, 8826 (2021).

[5] E. J. Sie et al., Nature 565, 61 (2019).