NMR ANALYSIS OF THE ELECTRONIC-STRUCTURE OF SUPERCONDUCTING YTTRIUM CARBIDE HALIDES

Nuclear magnetic resonance and relaxation are reported for C-13, Br-79 /81 and I-127 in the layered carbide halides Y2C2Br2, Y2C2Br0.5I1.5, Y 2C2I2 and Y2CBr2 for natural isotope abundances and for C-13-enriched samples, Field and temperature dependences of C-13 spin-lattice relaxa tion are derived. The data analysis supports p-like character of the c onduction electrons at the C-2 dumbbell sites in the superconducting d icarbides. Nonlinear temperature dependence of the C-13 Korringa rate in Y2C2Br2 indicates that the Fermi energy falls in a region of positi ve curvature of the energy-dependent density of states. (C) 1998 Elsev ier Science S.A.