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

Abstract

Laser excitation has emerged as a means to expose hidden states of matter and promote phase transitions on demand. Such laser-induced transformations are often rendered possible owing to the delivery of spatially and/or temporally manipulated light, carrying energy quanta well above the thermal background. Here, we report time-resolved broadband femtosecond (fs) transient absorption measurements on thin flakes of the Weyl semimetal candidate T d-MoTe2 subjected to various levels and schemes of fs-photoexcitation. Our results reveal that impulsive fs-laser irradiation alters the interlayer behavior of the low temperature T d phase as evidenced by the persistent disappearance of its characteristic coherent 1A1 ≈ 13 cm–1 shear phonon mode. We found that this structural transformation is likely related to lattice strain formation, withstands thermal cycling, and can be reverted to the 1T′ phase by fs-laser treatment at room temperature. Since interlayer shear strain was encountered to lead to a topologically distinct phase in an analogous compound, our work opens the door to the reversible optical control of electronic properties in this class of materials.

Photoinduced Structural Dynamics of 2H-MoTe2Under Extremely High-Density Excitation Conditions

“…T d is a low-temperature (<250 K) phase of 1T′. To date, ultrafast transient spectroscopic measurements have demonstrated the structural phase transition between the 1T′ and T d phases and the emergence of the intermediate T* phase. − Theoretical calculations have predicted the 2H-to-1T′ phase transition in the presence of a transient metallic 2H* phase under electronic excitation conditions at a magnitude of several percent. − Therefore, it is essential to investigate the structural dynamics of MoTe 2 in the experiment, which comprehensively interferes with photoexcited dense electron–hole plasma . However, there are few experimental studies on intense electronic excitation because photothermal and heat-accumulation effects often lead to permanent ablation and tellurium segregation .…”