Impact of random impurities on the anomalous Hall effect in chiral superconductors

TL;DR

This study investigates how random impurities affect the anomalous Hall effect in chiral superconductors, revealing that disorder can induce finite Hall responses in certain states and suppress intrinsic effects in multiband systems.

Contribution

It provides a real-space analysis of impurity effects on the Hall response in single-band and multiband chiral superconductors, highlighting differences from previous diagrammatic studies.

Findings

Single-band chiral p-wave reproduces previous Hall conductivity results.

Non-p-wave chiral states can exhibit finite Hall response with impurities.

Disorder suppresses intrinsic Hall conductivity in multiband superconductors.

Abstract

The anomalous Hall effect and the closely related polar Kerr effect are among the most direct evidence of chiral Cooper pairing in some superconductors. While it has been known that disorder or multiband pairing is typically needed for these effects to manifest, there is a lack of direct real-space investigation with regard to how disorder impacts the Hall response in both single-band and multiband chiral superconductors. On the basis of chiral superconducting models often adopted for \SRO, we study in this work the anomalous Hall effect in the presence of random non-magnetic impurities on real-space lattices. The single-band chiral p-wave ($p_x+ip_y$) calculation qualitatively reproduces the Hall conductivity obtained in previous skew-scattering-type diagrammatic analyses, along with some quantitative difference originating primarily from contributions involving impurity-induced in-gap states. The non-p-wave chiral states, such as $d_{x^2-y^2}+id_{xy}$, generically exhibit finite Hall response in the presence of random impurities, in contrast to a conclusion drawn from the aforementioned diagrammatic study. In particular, while pointlike impurities appears to induce minuscule Hall conductivity in non-self-consistent calculations, self-consistency and finite-range impurity potentials can both lead to substantial Hall conductivity. On the other hand, the intrinsic Hall conductivity in multiband chiral superconductors, which is related to interband transitions, decreases parametrically as disorder suppresses the superconducting order parameter. In addition, we check that random impurities do not induce anomalous Hall effect in non-chiral but time-reversal symmetry breaking superconducting states the likes of $s+i d_{x^2-y^2}$ and $d_{x^2-y^2}+i g_{xy(x^2-y^2)}$. We briefly remark on the implications of our results for Kerr effect measurements.