Superconductivity in a magnetically ordered background

Abstract

Borocarbide compounds with the formula RNi 2B 2C 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 HoNi 2B 2C.