Upper Critical Field of Two-Band Superconductors Containing Nonmagnetic Impurities. II

An approximate equation is derived that is satisfied by the upper critical field of two-band superconductors containing nonmagnetic impurities at temperatures just above zero. On the basis of this equation, it is found that if both the $s$ band and the $d$ band are in the superconducting phase, the upper critical field is larger than that of the two-band superconductor with the $d$ band in the superconducting phase and the $s$ band in the normal phase, at temperatures just above zero.