Nmr Spectra For A Nested Fermi-Liquid Model

The anomalous NMR relaxation rate and Knight shift in the YBa2Cu3O7 superconducting state contrast notably with conventional BCS theory for s-wave energy gap models. A d-wave energy gap on a nested Fermi surface with a large gap ratio 2 Delta(0) approximate to 11T(c) fits the data and is explained by using a temperature-dependent pairing interaction. A spin fluctuation pairing mechanism involves the susceptibility, which develops a T variation from electron collision damping. A superconducting energy gap reduces the damping below T-c, enhances the susceptibility, and therefore strengthens the pairing at low T.