Realizing T_d phase at room temperature in ultrathin MoTe₂

MoTe₂ emerges as a new type of transition metal dichalcogenide (TMD) whose differnet polymorphs show very different properties. In bulk MoT_e, both hexagonal 2H phase (semiconducting) and monmclinic 1T' phase (semimetallic) can be formed at room temperature depending on the growth conditions. When temperature is lowered to 250K, the 1T' phase transforms into an orthorhombic T_d phase in which the MoTe₂ crystal is a type-II Weyl semimetal with novel quantum phenomena. We exfoliated 1T'-MoTe₂ flakes on SiO₂ substrates and protected them with boron nitride from oxidation. Electrical transport measurements show that the ultrathin flakes do not show a phase transition below 250K. Raman studies reveal that the MoTe₂ ultrathin flakes exhibit a T_d phase even at room temperature, making it a potential host material for realizing type-II Weyl semimetal at room temperature.