Fermi surface topology and vortex state in MgB2

TL;DR

This paper models MgB2's Fermi surface to explain its anisotropic upper critical field behavior and vortex state properties, aligning theoretical predictions with experimental observations.

Contribution

It introduces a detailed Fermi surface model for MgB2 and explains the temperature dependence of Bc2 anisotropy using bandstructure parameters.

Findings

The Bc2 anisotropy's temperature dependence is explained by small c-axis dispersion.

Calculated density of states matches recent vortex state measurements.

The model highlights the role of small interband pairing interactions.

Abstract

Based on a detailed modeling of the Fermi surface topology of MgB2 we calculated the anisotropy of the upper critical field Bc2 within the two gap model. The sigma-band is modeled as a distorted cylinder and the pi-band as a half-torus, with parameters determined from bandstructure calculations. Our results show that the unusual strong temperature dependence of the Bc2 anisotropy, that has been observed recently, can be understood due to the small c-axis dispersion of the cylindrical Fermi surface sheets and the small interband pairing interaction as obtained from bandstructure calculations. We calculate the magnetic field dependence of the density of states within the vortex state for field in c-axis direction and compare with recent measurements of the specific heat on MgB2 single crystals.