NMR Study of⁹³Nb in Layered Superconducting 2H-NbSe₂

Abstract

The nuclear spin-lattice relaxation times T 1 's and the Knight shift of 93 Nb in 2H-NbSe 2 in a single crystal and powdered samples have been measured at 10 MHz and at low temperatures. The Knight shift contains both isotropic and anisotropic terms. The isotropic Knight shift, K iso =-0.03(%), is decomposed into the core-polarization part, K d =-0.66(%), and the orbital part, K orb =+0.63(%). In normal state, T 1 obeys a relation, T 1 T =65±10 msecK and shows no strong anisotropy. The dependence of T 1 on the symmetry properties of the conduction wave functions is discussed. It is concluded that the admixture of d 3 z 2 - r 2 orbit dominates at the Fermi level and T 1 of 93 Nb is dominated by the core-polarization interaction. In the superconducting state T 1 varies exponentially as in the case of bulk BCS superconductor with energy gap of 3.5 k B T C .