Eur. Phys. J. B 44, 183-188 (2005)
https://doi.org/10.1140/epjb/e2005-00113-8

Anisotropy of the upper critical field in MgB₂: the two-gap Ginzburg-Landau theory

Commissariat à l'Énergie Atomique, DSM/DRFMC/SPSMS, 17 avenue des Martyrs, 38054 Grenoble Cedex 9, France

Corresponding author: ^a dao@drfmc.ceng.cea.fr

Received: 26 August 2004
Revised: 26 January 2005
Published online: 20 April 2005

Abstract

The upper critical field in MgB₂ is investigated in the framework of the two-gap Ginzburg-Landau theory. A variational solution of linearized Ginzburg-Landau equations agrees well with the Landau level expansion and demonstrates that spatial distributions of the gap functions are different in the two bands and change with temperature. The temperature variation of the ratio of two gaps is responsible for the upward temperature dependence of in-plane as well as for the deviation of its out-of-plane behavior from the standard angular dependence. The hexagonal in-plane modulations of  can change sign with decreasing temperature.