Nuclear spin coherence in superconducting Nb$_3$Sn

TL;DR

This study uses $^{93}$Nb NMR to explore the normal and superconducting states of Nb$_3$Sn, revealing suppressed order parameters under magnetic fields and a strong, evolving RKKY interaction.

Contribution

It provides new insights into the electron-nuclear interactions and superconducting properties of Nb$_3$Sn through detailed NMR measurements.

Findings

Suppression of the superconducting order parameter by magnetic field.

Identification of a large electron-nuclear exchange interaction.

Evolution of the RKKY interaction from normal to superconducting states.

Abstract

We have investigated the normal and superconducting states of the technologically important compound Nb$_3$Sn using $^{93}$Nb nuclear magnetic resonance. From spin-lattice relaxation we find strong suppression of the zero-temperature superconducting order parameter by magnetic field. Additionally we have identified an anomalously large electron-nuclear exchange interaction from spin-spin relaxation measurements, an order of magnitude beyond that of the nuclear dipolar coupling. This RKKY interaction evolves from normal to superconducting states, becoming essentially Lorentzian in the low temperature limit.