Electronic States of Boron in Superconducting MgB${}_2$ Studied by ${}^{11}$B NMR

Abstract

NMR spectra and nuclear spin-lattice relaxation rate $T_1^{-1}$ of ${}^{11}$B have been measured in superconducting polycrystalline MgB${}_2$ with $T_C^{ons}\cong 39.5K$. It is shown that $(T_{1}T{)}^{-1}$ and the Knight shift $K_s$ are independent of temperature and nearly isotropic above $T_C$. Both of these quantities are decreased gradually in going to superconducting state. According NMR data the density of states (DOS) near the Fermi level is flat at the scale $\approx$ 500K. Some conclusions on the orbital content of the DOS at the Fermi level was done and compared with the results of the band structure calculations.

2 pages, 4 figures