Dimensionality-driven orthorhombic MoTe₂ at room temperature

We use variable-temperature Raman spectroscopy 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 by monitoring characteristic Raman lines from the orthorhombic phase. We propose a c-axis confinement mechanism to interpret this thickness-driven phase stabilization.