Enhancement of penetration field in vortex nanocrystals due to Andreev bound states

Abstract

We study the penetration field $H_{\mathrm{P}}$ for vortex nanocrystals nucleated in micron-sized samples with edges aligned along the nodal and anti-nodal directions of the d-wave superconducting parameter of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8-\delta }$. Here we present evidence that the $H_{\mathrm{P}}$ for nanocrystals nucleated in samples with edges parallel to the nodal direction is larger than for the antinodal case, $\sim 72$\,\% at low temperatures. This finding supports the theoretical proposal that surface Andreev bound states appearing in a sample with edges parallel to the nodal direction would produce an anomalous Meissner current that increases the Bean-Livingston barrier for vortex penetration.This has been detected thanks to the nucleation of vortex nanocrystals with a significant surface-to-volume ratio.

4 pages, 4 figures