Tunable spin-valley coupling in layered polar Dirac metals

TL;DR

This paper demonstrates that layered polar metals BaMnX2 (X=Bi, Sb) exhibit tunable spin-valley coupling in Dirac fermions, with experimental evidence showing how lattice distortions influence spin-valley configurations, opening avenues for spin-valleytronics.

Contribution

It reveals that BaMnX2 materials host tunable spin-valley-coupled Dirac fermions due to lattice polarization, expanding the possibilities beyond monolayer TMDCs.

Findings

BaMnBi2 has less lattice distortion than BaMnSb2.

Different spin-valley configurations are predicted and observed.

Experimental Shubnikov-de Haas oscillations confirm the tunability.

Abstract

In non-centrosymmetric metals, spin-orbit coupling (SOC) induces momentum-dependent spin polarization at the Fermi surfaces. This is exemplified by the valley-contrasting spin polarization in monolayer transition metal dichalcogenides (TMDCs) with in-plane inversion asymmetry. However, the valley configuration of massive Dirac fermions in TMDCs is fixed by the graphene-like structure, which limits the variety of spin-valley coupling. Here, we show that the layered polar metal BaMn$X_2$ ($X =$Bi, Sb) hosts tunable spin-valley-coupled Dirac fermions, which originate from the distorted $X$ square net with in-plane lattice polarization. We found that in spite of the larger SOC, BaMnBi$_2$ has approximately one-tenth the lattice distortion of BaMnSb$_2$, from which a different configuration of spin-polarized Dirac valleys is theoretically predicted. This was experimentally observed as a clear difference in the Shubnikov-de Haas oscillation at high fields between the two materials. The chemically tunable spin-valley coupling in BaMn$X_2$ makes it a promising material for various spin-valleytronic devices.