Chiral Current Inversion Induced by Flat-Band Andreev Bound States

TL;DR

This paper investigates how flat-band Andreev bound states can induce a reversal of chiral surface currents in certain three-dimensional chiral superconductors, revealing a novel interplay between surface states and current direction.

Contribution

It demonstrates that flat-band Andreev bound states cause chiral current inversion in a ($d_{zx} + i d_{yz}$)-wave superconductor, a phenomenon not observed in ($p_{x} + i p_{y}$)-wave cases.

Findings

Chiral current reverses at top and bottom surfaces in ($d_{zx} + i d_{yz}$)-wave SC.

Flat-band Andreev bound states coexist with chiral surface states.

Magnetic field distribution differs significantly due to current reversal.

Abstract

We study the spontaneous chiral surface current circulating in a three-dimensional disk of a chiral superconductor (SC) utilizing the quasiclassical Eilenberger theory. We obtain spatial profiles of the chiral current for both a ($d_{zx} + i d_{yz}$)-wave and a ($p_{x} + i p_{y}$)-wave SCs (where the top and bottom surfaces of the disk are perpendicular to the $z$-axis). Whereas the chiral current for a ($p_{x} + i p_{y}$)-wave SC does not depend on $z$, a reversal of the chiral current takes place at the top and bottom surfaces in the case of a ($d_{zx} + i d_{yz}$)-wave SC. In this latter case, flat-band Andreev bound states appear at the top and bottom surfaces in addition to the chiral surface states at the lateral surface. The chiral current reversal is explained in terms of hybridization between the two types of Andreev bound states. As a result, the magnetic field around the disk differs drastically between the two cases.