Magnetic-field-induced density of states in MgB2:: Spin susceptibility measured by conduction-electron spin resonance -: art. no. 012511

The magnetic-field dependence of the electron spin susceptibility chi(s) was measured in the superconducting state of high-purity MgB2 fine powders from the intensity of the conduction-electron spin resonance at 3.8, 9.4, and 35 GHz. The measurements confirm that a large part of the density of states is restored at low temperatures at fields below 1 T in qualitative agreement with the closing of the pi band gaps in the two-band model. However, the increase of chi(s) with field and temperature is larger than expected from current superconductor models of MgB2.