Topological Ladders in Transition-Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) host a rich variety of material properties, from spin-orbit coupled semiconductors to charge density-wave systems and superconductors [1,2]. The stabilisation of their varied ground states is largely thought to be driven by d-orbital physics of their transition-metal derived bands. Here, by combining spin- and angle-resolved photoemission spectroscopy (ARPES) with first-principles calculations, we show that band inversions within the chalcogen p-orbital manifold alone can cause TMDs to also host topological phenomena. First, we uncover a 3D tilted Dirac fermion and multiple topologically non-trivial surface states within the model system 1T-PdTe$_2$ where the p- and d-orbital bands are well separated in energy. We show, however, that the same topological signatures persist even within the more well-studied, d-band dominated members of the TMD classification. Through this, we firmly establish non-trivial band topologies as a generic feature of transition-metal dichalcogenides. [1] X. Xu, Nature Phys. 10 (2014) 343; [2] M. Chhowalla, Nature Chem. 5 (2013) 263.