Surface superconducting states in yttrium hexaboride single crystal in a tilted magnetic field

TL;DR

This study investigates surface superconducting states in yttrium hexaboride single crystals under tilted magnetic fields, revealing a higher than expected ratio of surface to bulk critical fields, challenging existing theoretical predictions.

Contribution

It provides experimental measurements of surface superconductivity in YB₆ with a novel technique, showing a ratio of Hc3 to Hc2 that exceeds theoretical expectations.

Findings

Hc3/Hc2 ratio is approximately 1.28 in the perpendicular direction.

The observed ratio surpasses the theoretical value of 1.

Surface roughness does not account for the discrepancy.

Abstract

We present the results of an experimental study of the nucleation of superconductivity at the surface of a single crystal YB$_6$ in a tilted dc magnetic field. A recently developed experimental technique allowed us to determine $H_{c3}$ at each side of the sample as a function of the angle between the dc magnetic field and the surface. Experiment shows that the ratio $H_{c3}/ H_{c2}\approx 1.28 $ in the direction perpendicular to the surface dc field while according to the theory this ratio should be equal to 1. This sharp distinction cannot be ascribed to the surface roughness.