  Temperature dependence of the lower critical field Hc1 (T) for the
superconducting magnesium diboride, MgB2, is studied in the vicinity of Tc by
using a two-band Ginzburg-Landau (G-L) theory. Theoretically calculated Hc1 (T)
near Tc exhibits a negative curvature. The results are shown to be in a good
agreement with the experimental data. In addition, two-band G-L theory
calculations give a temperature dependence of the Ginzburg-Landau parameter,
which varies little with temperature as in a similar manner of the microscopic
single-band BSC theory.
