Ginzburg-Landau Analysis on the Superconductivity in TlNi2Se2

Based on a 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 20m _e while that of the other band is only 0.6m _e. This semi-heavy-fermion feature can qualitatively explain the experimental value of the Kadowaki-Woods ratio in TlNi₂Se₂.