Anisotropy of the upper critical field in MgB2: the two-gap Ginzburg-Landau theory
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 Hc2 
as well as for the deviation of its out-of-plane behavior from the standard angular dependence. 
The hexagonal in-plane modulations of Hc2 can change sign with decreasing temperature. 
 
