Microscopic parameters of a type-II superconductor measured by small-angle neutron scattering

TL;DR

This paper reports the first measurements of microscopic parameters of a type-II superconductor, niobium, using small-angle neutron scattering, providing new insights into superconductivity mechanisms.

Contribution

It introduces a novel application of SANS to measure key microscopic parameters in a superconductor, advancing understanding of their roles.

Findings

First measurements of $R_0$, $r_i$, and $n_{cp}$ in niobium using SANS.

Comparison of SANS with other measurement methods.

Implications for studying superconductivity mechanisms.

Abstract

A necessary condition for understanding and predicting the properties of any material is knowledge of microscopic parameters which control these properties in a state of thermodynamic equilibrium. One can show (see, e.g., Ref.\,\cite{VK_book}), that in superconductors these parameters are the radius of the orbital motion of electrons bound in Cooper pairs $R_0$ and the radius of the field-induced currents $r_i$ caused by precession of the pairs; one more parameter, associated with $r_i$, is the number density of Cooper pairs $n_{cp}$. In this paper we report on the first measurements of these parameters in a type-II superconductor (niobium) by SANS (small-angle neutron scattering). Other approaches to measuring the microscopic parameters are considered. Our work suggests novel avenues for studying superconductivity, important for disclosing its mechanisms in superconductors of all kinds.