Chiral Current Inversion Induced by Flat-Band Andreev Bound States

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.