Evidence for Cooper Pair Diffraction on the Vortex Lattice of Superconducting Niobium

TL;DR

This study uses muon spin rotation to observe how Cooper pairs diffract on the vortex lattice in pure Niobium, revealing deviations from Ginzburg-Landau theory and supporting Delrieu's prediction for clean superconductors.

Contribution

First experimental evidence of Cooper pair diffraction on the vortex lattice in a superconductor, validated through SR measurements and theoretical analysis.

Findings

Deviations from Ginzburg-Landau predictions at low temperatures.

Observation of a conical shape in the magnetic field variation.

Support for Delrieu's theory of Cooper pair diffraction.

Abstract

We investigated the Abrikosov vortex lattice (VL) of a pure Niobium single crystal with the muon spin rotation (\mu SR) technique. Analysis of the \mu SR data in the framework of the BCS-Gor'kov theory allowed us to determine microscopic parameters and the limitations of the theory. With decreasing temperature the field variation around the vortex cores deviates substantially from the predictions of the Ginzburg-Landau theory and adopts a pronounced conical shape. This is evidence of partial diffraction of Cooper pairs on the VL predicted by Delrieu for clean superconductors.