Direct evidence of hidden local spin polarization in a centrosymmetric superconductor LaO$_{0.55}$F$_{0.45}$BiS$_2$

TL;DR

This study provides direct spectroscopic evidence of local spin polarization and coexistence of Rashba- and Dresselhaus-like spin textures in a centrosymmetric superconductor, revealing new insights into spin-orbit interactions and superconductivity.

Contribution

It is the first to experimentally observe local spin polarization and mixed spin textures in LaO$_{0.55}$F$_{0.45}$BiS$_2$, a centrosymmetric superconductor, using high-resolution spin- and angle-resolved photoemission spectroscopy.

Findings

Direct evidence of local spin polarization near the X point.

Observation of coexistence of Rashba-like and Dresselhaus-like spin textures.

Identification of spin-momentum locking Fermi surface in the superconductor.

Abstract

Conventional Rashba spin polarization is caused by the combination of strong spin-orbit interaction (SOI) and spatial inversion asymmetry. However, Rashba- and Dresselhaus-type spin-split states are predicted in LaOBiS$_2$ system by recent theory even though the crystal structure is centrosymmetric, which stem from the local inversion asymmetry of active BiS$_2$ layer. By performing high-resolution spin- and angle-resolved photoemission spectroscopy, we have investigated the electronic band structure and spin texture of superconductor LaO$_{0.55}$F$_{0.45}$BiS$_2$. Our studies present direct spectroscopic evidence for the local spin polarization in the vicinity of X point of both valence band and conduction band. Especially the coexistence of Rashba-like and Dresselhaus-like spin textures has been observed in the conduction band for the first time. The finding is of key importance for fabrication of proposed dual-gated spin-field effect transistor (SFET). Moreover, the spin-split band leads to a spin-momentum locking Fermi surface from which novel superconductivity emerges. Our demonstration not only expands the scope of spintronic materials but also enhances the understanding of SOI related superconductivity.