Effects of Strong Magnetic Fields on Pairing Fluctuations in High Temperature Superconductors

TL;DR

This paper develops a theoretical framework to understand how superconducting pairing fluctuations influence NMR measurements in high magnetic fields, aiding in clarifying the pseudogap's origin in high-T_c cuprates.

Contribution

It introduces a theory for pairing fluctuation effects on NMR relaxation and Knight shift, distinguishing between s-wave and d-wave fluctuations in layered high-T_c superconductors.

Findings

Recent experiments in YBa_2Cu_3O_{7-d} are explained by d-wave pairing fluctuations.

Orthorhombic distortion accounts for NQR and NMR relaxation rate discrepancies.

Proposes NMR experiments to differentiate s-wave and anisotropic pairing fluctuations.

Abstract

We present the theory for the effects of superconducting pairing fluctuations on the nuclear spin-lattice relaxation rate, 1/T_1, and the NMR Knight shift for layered superconductors in high magnetic fields. These results can be used to clarify the origin of the pseudogap in high-T_c cuprates, which has been attributed to spin fluctuations as well as pairing fluctuations. We present theoretical results for s-wave and d-wave pairing fluctuations and show that recent experiments in optimally doped YBa_2Cu_3O_{7-d} are described by d-wave pairing fluctuations. In addition, we show that the orthorhombic distortion in YBa_2Cu_3O_{7-d} accounts for an experimentally observed discrepancy between 1/T_1 obtained by NQR and NMR at low field. We propose an NMR experiment to distinguish a fluctuating s-wave order parameter from a fluctuating strongly anisotropic order parameter, which may be applied to the system Nd_{2-x}Ce_xCuO_{4-d} and possibly other layered superconductors.