Non-empirical calculations of temperature and angle dependences of upper critical fields for MgB2

The temperature and angle dependences of upper critical fields for MgB2 are estimated within a clean-limit weak-coupling theory using the electronic structure data obtained by the first-principles calculations. It is found that the field direction dependences of Hc2 deviate from the prediction of primitive Ginzburg-Landau theory at low temperature. It reflects the characteristics of the Fermi surface geometry. It is also found that the calculated Hc2 shows small in-plane anisotropy at low temperature.