Theoretical Analysis On The Electromagnetic Properties Of Two-gap Isotropic Superconductors

In 2001 Japanese scientists discovered that the binary compound MgB2 becomes superconducting at a high temperature about 39 K. Since then, it has been verified that MgB2 exhibits two superconducting energy gaps from many experiments, such as electronic tunneling spectrum, specific heat measurement and angle-resolved photoemission spectrum. This discovery has aroused the huge interest of research on two-gap superconductors all over the world, and various theoretical models of two-gap superconductivity are proposed up to now. Based on two-band isotropic Ginzburg-Landau theory, we study the magnetic properties of the recently observed superconducting crystal TlNi2Se2. Our exact solution of upper critical field reproduces the experimental data in a broad temperature range. It directly underlies the multi-gap superconductivity in this crystal. We also show that the effective mass of the electron for one band is about 20me while that of the other band is only 0.6me. This semi-heavy-fermion feature can qualitatively explain the experimental value of the Kadowaki-Woods ratio in TlNi2Se2. We further analysize another two-gap superconducting material SrPt3P.