Weak spin-orbit interactions induce exponentially flat mini-bands in magnetic metals without inversion symmetry

TL;DR

Weak spin-orbit interactions in non-centrosymmetric magnetic metals can create exponentially flat minibands on the Fermi surface, significantly affecting electron dynamics and observable electromagnetic properties.

Contribution

This work reveals how small spin-orbit coupling effects induce exponentially flat minibands in magnetic metals lacking inversion symmetry, a novel band-structure phenomenon.

Findings

Formation of exponentially flat minibands with bandwidth ~exp(-1/√delta)

Minibands cover a broad belt of width √delta on the Fermi surface

Pronounced features in the anomalous skin effect due to band-structure effects

Abstract

In metallic magnets like MnSi the interplay of two very weak spin-orbit coupling effects can strongly modify the Fermi surface. In the absence of inversion symmetry even a very small Dzyaloshinsky-Moriya interaction of strength delta<<1 distorts a ferromagnetic state into a chiral helix with a long pitch of order 1/delta. We show that additional small spin-orbit coupling terms of order delta in the band structure lead to the formation of exponentially flat minibands with a bandwidth of order exp(-1/sqrt(delta)) parallel to the direction of the helix. These flat minibands cover a rather broad belt of width sqrt(delta) on the Fermi surface where electron motion parallel to the helix practically stops. We argue that these peculiar band-structure effects lead to pronounced features in the anomalous skin effect.