Spin chirality and fermion stirring in topological bands

TL;DR

This paper shows that orbital currents in metals with broken time reversal symmetry induce spin chirality even without spin-dependent interactions, providing a new way to detect topological phases.

Contribution

It introduces a diagrammatic derivation of spin chirality from orbital currents and proposes local detection methods for topological superconducting phases.

Findings

Orbital currents generate spin chirality in metals.

Chirality leads to a chiral three-spin RKKY interaction.

Local probes can detect TRS breaking and topological phases.

Abstract

We demonstrate that in metals, both normal and superconducting, orbital currents present in the ground state when time reversal symmetry (TRS) is broken, generate spin chirality. Nonzero chirality can emerge in the absence of any spin-dependent interactions, even when the ground state remains spin-unpolarized. The chirality effect is derived diagrammatically and illustrated for Haldane model and the topological superconductivity problem. Chirality in the carrier band results in a chiral three-spin RKKY interaction between localized spins coupled to carriers by s-d Hamiltonian, an effect that can be detected by local probes such as spin-sensitive STM. In systems where detecting TRS breaking by conventional means is challenging, such as topological superconductors, local detection of spin chirality can serve as a reliable diagnostic of superconducting topological phases.