Surface Contribution to the Superconducting Properties of MgB2 Single Crystals

TL;DR

This study provides direct evidence of surface superconductivity in MgB2 single crystals, revealing non-Ohmic and angular-dependent resistivity near the critical field, supported by multiple experimental approaches.

Contribution

It presents new experimental evidence of surface superconductivity in MgB2, highlighting the surface's role in its superconducting properties.

Findings

Surface superconductivity observed on MgB2 crystals

Resistivity shows non-Ohmic behavior near Hc2^c

Angular dependence indicates surface effects

Abstract

We demonstrate direct evidence of possible surface superconductivity on small, well-shaped MgB2 single crystals. Transport measurements in the range H < 1.6 Hc2^c, where Hc2^c is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular dependent resistivity. Studies of the alignment of H with selected crystal surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.