Observation of Dirac surface states in the noncentrosymmetric superconductor BiPd

TL;DR

This study combines experimental and theoretical methods to reveal Dirac surface states with large spin splitting in the noncentrosymmetric superconductor BiPd, highlighting the effects of strong spin-orbit coupling and broken inversion symmetry.

Contribution

It provides the first detailed observation of Dirac surface states with large spin splitting in BiPd, emphasizing the role of SOC and noncentrosymmetry in shaping surface state properties.

Findings

Detection of multiple Dirac surface states in BiPd

Observation of extremely large spin splitting in surface states

Surface states differ significantly between opposite crystal faces

Abstract

Materials with strong spin-orbit coupling (SOC) have in recent years become a subject of intense research due to their potential applications in spintronics and quantum information technology. In particular, in systems which break inversion symmetry, SOC facilitates the Rashba-Dresselhaus effect, leading to a lifting of spin degeneracy in the bulk and intricate spin textures of the Bloch wave functions. Here, by combining angular resolved photoemission (ARPES) and low temperature scanning tunneling microscopy (STM) measurements with relativistic first-principles band structure calculations, we examine the role of SOC in single crystals of noncentrosymmetric BiPd. We report the detection of several Dirac surface states, one of which exhibits an extremely large spin splitting. Unlike the surface states in inversion-symmetric systems, the Dirac surface states of BiPd have completely different properties at opposite faces of the crystal and are not trivially linked by symmetry. The spin-splitting of the surface states exhibits a strong anisotropy by itself, which can be linked to the low in-plane symmetry of the surface termination.