Giant spin Hall effects and topological surface states in ternary-layered MAX carbides Mn+1AlCn (M= Nb, Ta, n=1, 2, 3)

TL;DR

This study reveals giant spin Hall effects and topological surface states in layered MAX carbides Mn+1AlCn, highlighting their potential for efficient charge-to-spin conversion in spintronic applications.

Contribution

It provides a systematic analysis of the electronic structures, band topology, and spin Hall effects in Mn+1AlCn MAX carbides, identifying topological surface states and giant SHE in these materials.

Findings

M3AlC2 and M4AlC3 exhibit Dirac-band-crossings and nodal lines without SOC.

Including SOC opens gaps and yields nontrivial Z2 topological invariants.

Ta3AlC2 shows a giant spin Hall angle of ~60%.

Abstract

In this work, we report a systematic study of the electronic structures, band topology, and intrinsic spin Hall effect (SHE) of the layered MAX carbides Mn+1AlCn (M= Nb, Ta, n=1, 2, 3) and explore the correlation effects on the SHE. The results show that M3AlC2 and M4AlC3 (M= Nb, Ta) share similar Dirac-band-crossing features near the Fermi level (EF) and form nodal lines in the absence of spin-orbit coupling (SOC). When the SOC is included, the Dirac band crossings are fully gapped, resulting in nontrivial Z2 topological invariants (1;000) with a pair of surface states on the (001) plane. Remarkably, the multiple gapped Dirac points contribute to locally strong spin Berry curvatures, which lead to large spin Hall conductivities and a giant spin Hall angle up to ~ 60% for Ta3AlC2. Moreover, we also elucidate the impact of Hubbard U correction on SHC. Our findings indicate that Ta3AlC2 might represent an intriguing layered Z2 topological metal with superior charge-to-spin conversion efficiency.