Coexistence of 2D hole and 3D electron in a topological insulator candidate: T' - WSe2.

1T’ Transition metal dichalcogenides (TMDs) exhibit various topological states such as Fermi arcs in the bulk and 2D quantum spin hall insulator states in the monolayer. However, exploration into pristine 1T’ TMDs beyond MoTe2 and WTe2 (e.g. T’-WSe2 or T’-MoS2) has been difficult due to the metastability of the T’ phase.

Here, we present the gap state and thermal activated charge transport in the few-layer (FL) T'-WSe2, exfoliated from a topological semimetal 2M-WSe2 bulk crystal. In contrast to its hexagonal counterpart with bandgap of 1.7 eV, FL T'- WSe2 shows metallic behavior at high temperature and presents a gap with size of meV. Further, we will discuss the band gap closing behavior with the displacement field.



We then present the landau fan diagram in bi-layer T'-WSe2 with magneto transport studies under perpendicular magnetic field up to 42 T. At the high field, the longitudinal resistance evolves to quantum oscillation and enters the quantum hall state with Rxx = 0 at the hole side. On the other hand, the electron side shows quantum oscillation and landau level crossing at high doping density. Finally, we will discuss the LL degeneracy and spin-orbit coupling in FL T'- WSe2.