Dimensionality-driven orthorhombic MoTe2 at room temperature

Abstract

We use a combination of Raman spectroscopy and transport measurements to study thin flakes of the type-II Weyl semimetal candidate MoTe2 protected from oxidation. In contrast to bulk crystals, which undergo a phase transition from monoclinic to the inversion symmetry breaking, orthorhombic phase below ~250 K, we find that in moderately thin samples below ~12 nm, a single orthorhombic phase exists up to and beyond room temperature. This could be due to the effect of c-axis confinement, which lowers the energy of an out-of-plane hole band and stabilizes the orthorhombic structure. Our results suggest that Weyl nodes, predicated upon inversion symmetry breaking, may be observed in thin MoTe2 at room temperature.