Spin chirality and fermion stirring in topological bands

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.