NMR spectra for a nested Fermi-liquid model

Abstract

The anomalous NMR relaxation rate and Knight shift in the YBa{sub 2}Cu{sub 3}O{sub 7} 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}{sub 0}{approx}11T{sub c} fits the data and is explained by using a {ital 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{sub c}, enhances the susceptibility, and therefore strengthens the pairing at low T. {copyright} {ital 1997} {ital The American Physical Society}