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Abstract:

Layered SnAs‐based Zintl compounds exhibit a distinctive electronic structure, igniting extensive research efforts in areas of superconductivity, topological insulators, and quantum magnetism. In this paper, the crystal structures and electronic properties of the Zintl compound SrSn2As2 upon compression are systematically investigated. Pressure‐induced superconductivity is observed in SrSn2As2 with a nonmonotonic evolution of superconducting transition temperature Tc. Theoretical calculations together with high‐pressure synchrotron X‐ray diffraction and Raman spectroscopy have identified that SrSn2As2 undergoes a structural transformation from a rhombohedral R 3 ¯ $\bar{3}$ m phase to the monoclinic C2/m phase. Beyond 28.3 GPa, Tc is suppressed due to a reduction of the density of state (DOS) at the Fermi level. The discovery of pressure‐induced superconductivity, accompanied by structural transitions in SrSn2As2, greatly expands the physical properties of layered SnAs‐based compounds and provides new ground states upon compression.

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.