Surface critical field of MgB2:: the two-band Ginzburg-Landau theory

We investigate the surface critical field H-c3 of MgB2 in the clean limit using the two-band Ginzburg-Landau (GL) theory. When the surface of a superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field (H) over right arrow, the ratio H-c3/H-c2 ( where H-c2 is the upper critical field of MgB2) exhibits strong temperature dependence. When the surface of a superconductor coincides with the bc plane and is parallel to (H) over right arrow, the ratio depends not only on temperature, but also on the angle between the c axis and (H) over right arrow. However, for single-band superconductors this ratio is constant.