  Manipulating crystal structure and the corresponding electronic properties in
quantum materials provides opportunities for the exploration of exotic physics
and practical applications. Here, by ultrafast electron diffraction, structure
factor calculation and TDDFT-MD simulations, we report the photoinduced
concurrent intralayer and interlayer structural transitions in the Td and 1T'
phase of XTe2 (X=Mo, W). Concomitant with the interlayer structural transition
by shear displacement, the ultrafast suppression of the intralayer Peierls
distortion within 0.3 ps is demonstrated and attributed to Mo-Mo (W-W) bond
stretching. We discuss the modification of multiple quantum electronic states
associated with the intralayer and interlayer structural transitions, such as
the topological band inversion and the higher-order topological state. The twin
structure and the stacking fault in XTe2 are identified by the ultrafast
structural response. Our work elucidates the pathway of the photoinduced
intralayer and interlayer structural transitions in atomic and femtosecond
spatiotemporal scale. Moreover, the concurrent intralayer and interlayer
structural transitions reveals the traversal of all double-well potential
energy surfaces (DWPES) by laser excitation in material system, which may be an
intrinsic mechanism in the field of photoexcitation-driven symmetry
engineering, beyond the single DWPES transition model and the order-disorder
transition model.
