Orbital-dependent two-band superconductivity in MgB2

TL;DR

This paper demonstrates that a two-band, k-dependent superconducting gap model accurately explains optical, thermodynamic, and magnetic properties of MgB2, highlighting the importance of anisotropy in understanding its superconductivity.

Contribution

It introduces a two-band anisotropic model with specific gap symmetries that better explains MgB2's properties than single-gap models.

Findings

Two-band model fits optical conductivity data.

Anisotropic gaps in sigma and pi bands are identified.

Single-gap models are insufficient for consistent explanation.

Abstract

We show that a two-band model with ${\bf k}$-dependent superconducting gaps well describes the transmission and optical conductivity measured for MgB$_2$ thin films. It is also shown that the two-band anisotropic model consistently describes the specific-heat jump and thermodynamic critical magnetic field $H_c$. A single-gap anisotropic model is shown to be insufficient to understand consistently optical and thermodynamic behaviors. In our model, the pairing symmetry in each band has an anisotropic characteristic which is determined almost uniquely; the superconducting gap in the $\sigma$-band has anisotropy in the ab-plane and the gap in the $\pi$-band has a prolate form exhibiting anisotropy in the c-direction. The anisotropy in the $\sigma$-band produces rather small effects on the physical properties compared to the anisotropy in the $\pi$-band.