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 MoTe2, where the low-temperature orthorhombic Td 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 1T′ to the Td phase, diffuse scattering accompanies the transition, arising from random, in-plane layer displacements, and dissipates upon entering the Td 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.