Temperature-driven topological transition in 1T'-MoTe2

The topology of Weyl semimetals requires the existence of unique surface states. Surface states have been visualized in spectroscopy measurements, but their connection to the topological character of the material remains largely unexplored. 1T'-MoTe2, presents a unique opportunity to study this connection. This material undergoes a phase transition at 240 K that changes the structure from orthorhombic (putative Weyl semimetal) to monoclinic (trivial metal), while largely maintaining its bulk electronic structure. Here, we show from temperature-dependent quasiparticle interference measurements that this structural transition also acts as a topological switch for surface states in 1T'-MoTe2. At low temperature, we observe strong quasiparticle scattering, consistent with theoretical predictions and photoemission measurements for the surface states in this material. In contrast, measurements performed at room temperature show the complete absence of the scattering wavevectors associated with the trivial surface states. These distinct quasiparticle scattering behaviors show that 1T'-MoTe2 is ideal for separating topological and trivial electronic phenomena via temperature-dependent measurements.Weyl semimetals: switching off topologyA temperature-induced structural phase transition can provide insight into the effect of Fermi arcs on the properties of Weyl semimetals. Weyl semimetals are topological materials at the surface of which Weyl points—the points at which electron and hole pockets touch—are connected in pairs by Fermi arc surface states. Probing the topological nature of the surface states has so far proven difficult, and a connection with the band structure of the material is complex to establish. An international team of researchers led by Abhay Pasupathy at Columbia University demonstrated, by combining experiments and theory, that the Weyl semimetal MoTe2 undergoes a temperature-driven structural phase transition that switches off the Weyl behavior. This makes it possible to systematically compare the electronic properties of the trivial and topological states.