Pressure-Induced Phase Transition in Weyl Semimetallic WTe₂

Tungsten ditelluride (WTe₂) is a semimetal with orthorhombic T_d phase that possesses some unique properties such as Weyl semimetal states, pressure-induced superconductivity, and giant magnetoresistance. Here, the high-pressure properties of WTe₂ single crystals are investigated by Raman microspectroscopy and ab initio calculations. WTe₂ shows strong plane-parallel/plane-vertical vibrational anisotropy, stemming from its intrinsic Raman tensor. Under pressure, the Raman peaks at ≈120 cm⁻¹ exhibit redshift, indicating structural instability of the orthorhombic T_d phase. WTe₂ undergoes a phase transition to a monoclinic T′ phase at 8 GPa, where the Weyl states vanish in the new T′ phase due to the presence of inversion symmetry. Such T_d to T′ phase transition provides a feasible method to achieve Weyl state switching in a single material without doping. The new T′ phase also coincides with the appearance of superconductivity reported in the literature.