Upper critical field $H_{c_2}$ in two-band superconductor

Abstract

It was obtained the equation for the definition of upper critical field in the system with two overlapping energetic bands on the Fermi surface, which is valid for the whole temperature interval $0\le T<T_c$. The analytic expressions for the value $H_{c_2}$ at $T\sim T_c$ and $T\ll T_c$ cases were defined. The possibility of changing the curvature $H_{c_2}(T)$ with changing of the electrons speed ratio $v_1/v_2$ on different cavities on the Fermi surface was revealed. It was obtained the qualitative accordance with experimental data for the intermetallic compound $Mg{B}_2$.

13 pages, 1 figure in the text