Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies

TL;DR

This study investigates the specific heat of MgB_2 single crystals, revealing evidence for two-band superconductivity with distinct anisotropies and multiple critical fields, advancing understanding of its superconducting properties.

Contribution

It provides experimental evidence supporting two-band superconductivity in MgB_2, highlighting different anisotropies and the necessity of three critical fields to describe its superconducting state.

Findings

Evidence for two-band superconductivity with different anisotropies.

Identification of three distinct upper critical fields.

Confirmation of isotropic small-gap band and anisotropic large-gap band.

Abstract

Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the small gap being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2.