Electronic states of boron in superconducting MgB2 studied by11B NMR

Nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rateT1−1 of11B have been measured in superconducting polycrystalline MgB2 with 7cons = 39.5 K. It is shown that (T1T−1 and the Knight shiftKs are independent of temperature and nearly isotropic aboveTc. Both of these quantities are decreased gradually in going to the superconducting state. According to NMR data the density of states near the Fermi level is flat at the scale of about 500 K. Some conclusions on the orbital content of the density of states at the Fermi level were drawn and compared with the results of the band structure calculations.