Superconductivity in a magnetically ordered background

TL;DR

This paper extends BCS theory to analyze how magnetic order in borocarbide compounds affects superconductivity, considering various magnetic structures and providing qualitative criteria for their interplay.

Contribution

It introduces an extension of BCS theory to systems with magnetic order, including incommensurate phases, and analyzes the influence of magnetic structures on superconductivity.

Findings

Magnetic order's impact on superconductivity varies with structure and electron bands.

Qualitative criteria for magnetic-superconducting coexistence are proposed.

Application to HoNi2B2C illustrates the theory's relevance.

Abstract

Borocarbide compounds with the formula RNi2B2C show interesting superconducting and magnetic properties and the coexistence of the two phenomena. BCS theory is extended to systems with underlying commensurate magnetic order. In the case of helical phases the technique may be extended to any Q-vector and there exists a well defined limit for incommensurate values. The way magnetic order influences superconductivity depends crucially on the details of both the magnetic structure and the electron bands, but some qualitative criteria may be given. As an example we give a brief analysis of the compound HoNi2B2C.