Electronic structures and photoemission spectroscopy

Abstract:

The (Bi₂)_m(Bi₂Te₃)_n homologous series possess natural multilayer heterostructure with intriguing physical properties at ambient pressure. Herein, we report the pressure-dependent evolution of the structure and electrical transport of the dual topological insulator BiTe, a member of the (Bi₂)_m(Bi₂Te₃)_n series. With applied pressure, BiTe exhibits several different crystal structures and distinct superconducting states, which is remarkably similar to other members of the (Bi₂)_m(Bi₂Te₃)_n series. Our results provide a systematic phase diagram for the pressure-induced superconductivity in BiTe, contributing to the highly interesting physics in this (Bi₂)_m(Bi₂Te₃)_n series.

Abstract:

We report on the interplay between a van Hove singularity and a charge density wave state in 2⁢𝐻−TaSe2. We use angle-resolved photoemission spectroscopy to investigate changes in the Fermi surface of this material under surface doping with potassium. At high doping, we observe modifications which imply the disappearance of the (3×3) charge density wave and formation of a different correlated state. Using a tight-binding-based approach as well as an effective model, we explain our observations as a consequence of coupling between the single-particle Lifshitz transition during which the Fermi level passes a van Hove singularity and the charge density order. In this scenario, the high electronic density of states associated with the van Hove singularity induces a change in the periodicity of the charge density wave from the known (3×3) to a new (2×2) superlattice.