  Recent development of ultrashort laser pulses allows for optical control of
structural and electronic properties of complex quantum materials. The layered
transition metal dichalcogenide MoTe2, which can crystalize into several
different structures with distinct topological and electronic properties,
provides possibilities to control or switch between different phases. In this
study we report a photo-induced sub-picosecond structural transition between
the type-II Weyl semimetal phase and normal semimetal phase in bulk crystalline
MoTe2 by using ultrafast pump-probe and time-resolved second harmonic
generation spectroscopy. The phase transition is most clearly characterized by
the dramatic change of the shear oscillation mode and the intensity loss of
second harmonic generation. This work opens up new possibilities for ultrafast
manipulation of the topological properties of solids, enabling potentially
practical applications for topological switch device with ultrafast
excitations.
