Charge transfer and Spin-Valley locking in 4Hb-TaS${}_2$

Abstract

4Hb-TaS${}_2$ is a superconductor that exhibits unique characteristics such as time-reversal symmetry breaking, hidden magnetic memory, and topological edge modes. It is a naturally occurring heterostructure comprising of alternating layers of 1H-TaS${}_2$ and 1T-TaS${}_2$. The former is a well-known superconductor, while the latter is a correlated insulator with a possible non-trivial magnetic ground state. In this study, we use angle resolved photoemission spectroscopy to investigate the normal state electronic structure of this unconventional superconductor. Our findings reveal that the band structure of 4H-TaS${}_2$ fundamentally differs from that of its constituent materials. Specifically, we observe a significant charge transfer from the 1T layers to the 1H layers that drives the 1T layers away from half-filling. In addition, we find a substantial reduction in inter-layer coupling in 4Hb-TaS${}_2$ compared to the coupling in 2H-TaS${}_2$ that results in a pronounced spin-valley locking within 4Hb-TaS${}_2$