Robust weak antilocalization due to spin-orbital entanglement in Dirac material Sr3SnO

H Nakamura,D Samal,P Ostrovsky,H Takagi,D Huang,J Merz,A Yaresko,E Khalaf

doi:10.1038/s41467-020-14900-1

Abstract

The presence of both inversion (P) and time-reversal (T) symmetries in solids leads to a double degeneracy of the electronic bands (Kramers degeneracy). By lifting the degeneracy, spin textures manifest themselves in momentum space, as in topological insulators or in strong Rashba materials. The existence of spin textures with Kramers degeneracy, however, is difficult to observe directly. Here, we use quantum interference measurements to provide evidence for the existence of hidden entanglement between spin and momentum in the antiperovskite-type Dirac material Sr3SnO. We find robust weak antilocalization (WAL) independent of the position of EF. The observed WAL is fitted using a single interference channel at low doping, which implies that the different Dirac valleys are mixed by disorder. Notably, this mixing does not suppress WAL, suggesting contrasting interference physics compared to graphene. We identify scattering among axially spin-momentum locked states as a key process that leads to a spin-orbital entanglement.

Highlights

The presence of both inversion (P) and time-reversal (T) symmetries in solids leads to a double degeneracy of the electronic bands (Kramers degeneracy)
Magnetic field breaks time-reversal symmetry required for the interference, providing a sensitive probe for the quantum interference: a positive magnetoconductance follows as a result of weak localization (WL) (WAL)
Intervalley scattering causes a crossover from the symplectic time-reversal symmetry, which characterizes the emergent degrees of freedom in individual valleys, to orthogonal time-reversal symmetry, which characterizes the microscopic degrees of freedom

Summary

Introduction

The presence of both inversion (P) and time-reversal (T) symmetries in solids leads to a double degeneracy of the electronic bands (Kramers degeneracy). The presence of a Berry curvature in momentum space may lead to an extra phase shift of π for such closed trajectories, resulting in weak antilocalization (WAL), as demonstrated for graphene[4,5,6,7,8] This phase shift is a direct consequence of pseudospin-momentum locking. The band degeneracy induced by the existence of inversion (P) and time-reversal (T) symmetries in the absence of spin-rotation symmetry makes spin–orbit coupled Dirac materials unique in comparison with both graphene, where spin is conserved, and Weyl semimetals such as TaAs20–23, where the band degeneracy is lifted due to the broken T or P symmetries. Quantum interference measurements are ideally suited to detect such hidden entanglement in Dirac materials, since WAL is expected whenever spin symmetry is broken, regardless of the existence of PT symmetry

Methods

Results

Conclusion