Hidden non-collinear spin-order induced topological surface states

TL;DR

This study provides direct experimental evidence of non-collinear antiferromagnetic order in NdSb, linking it to the emergence of topological surface states and revealing a hidden spin-rotation transition affecting the material's electronic topology.

Contribution

It reports the first direct observation of non-collinear antiferromagnetic order and a hidden spin-rotation transition in NdSb, elucidating their roles in topological surface state emergence.

Findings

Non-collinear antiferromagnetic order observed via spin-polarized STM.

Hidden spin-rotation transition coincides with surface state splitting.

Multiple modulations cause band splitting and topological band inversion.

Abstract

Rare-earth monopnictides are a family of materials simultaneously displaying complex magnetism, strong electronic correlation, and topological band structure. The recently discovered emergent arc-like surface states in these materials have been attributed to the multi-wave-vector antiferromagnetic order, yet the direct experimental evidence has been elusive. Here we report the observation of non-collinear antiferromagnetic order with multiple modulations using spin-polarized scanning tunneling microscopy. Moreover, we discover a hidden spin-rotation transition of single-to-multiple modulations 2 K below the Neel temperature. The hidden transition coincides with the onset of the surface states splitting observed by our angle-resolved photoemission spectroscopy measurements. Single modulation gives rise to a band inversion with induced topological surface states in a local momentum region while the full Brillouin zone carries trivial topological indices, and multiple modulation further splits the surface bands via non-collinear spin tilting, as revealed by our calculations. The direct evidence of the non-collinear spin order in NdSb not only clarifies the mechanism of the emergent topological surface states, but also opens up a new paradigm of control and manipulation of band topology with magnetism.