Relaxation of Nuclear Magnetic Moments and Site-Selective NMR in d-Wave Superconductors

TL;DR

This paper introduces a new relaxation mechanism for nuclear magnetic moments in d-wave superconductors, explaining NMR results without requiring antiferromagnetic order in vortex cores.

Contribution

It identifies a novel relaxation process involving spin-polarized quasiparticles that dominates at low temperatures in type-II d-wave superconductors.

Findings

Theoretical results match NMR experiments on YBCO in high magnetic fields.

The relaxation mechanism does not require antiferromagnetic order in vortex cores.

Provides a new understanding of nuclear spin relaxation in high-temperature superconductors.

Abstract

A new mechanism for relaxing the nuclear magnetic moments, in which a pair of spin-polarized BCS quasiparticles is emitted or absorbed, and which dominates at low temperature, is identified in type-II d-wave superconductors in an external magnetic field above Hc1. The results of the theory are compared with the NMR experiments on YBCO in high magnetic fields and found to agree without invoking antiferromagnetic order in the vortex core.