Emergence of topologically protected states in the MoTe2 Weyl semimetal with layer-stacking order

Electronic tunability in crystals with weakly bound layers can be achieved through layer stacking order. One such example is ${\mathrm{MoTe}}_{2}$, where the low-temperature orthorhombic ${T}_{d}$ phase is topological and host to Weyl quasiparticles. The transition mechanism to the nontrivial topology is elucidated by single-crystal neutron diffraction. Upon cooling from the monoclinic $1{T}^{\ensuremath{'}}$ to the ${T}_{d}$ phase, diffuse scattering accompanies the transition, arising from random, in-plane layer displacements, and dissipates upon entering the ${T}_{d}$ phase. Diffuse scattering is observed only in the $H0L$ plane due to irreversible layer shifts along the $c$ axis that break the centrosymmetry of the monoclinic lattice.