The superconducting phases of UPt 3

Abstract

The heavy-fermion superconductor UPt 3 shows many indications of unconventional superconductivity. In particular, the multiplicity of superconducting phases calls for an explanation in terms of a multi-component order parameter. As will be reviewed in this article, these phases have been mapped out recently by a number of different measurements. The existence of a tetracritical point in the field—temperature ( B, T) plane for B ⊥ c and B | c is consistent with thermodynamic constraints. The specific heat under pressure indicates a strong relation between superconductivity and the weak antiferromagnetic order. The recent observation of a structural modulation and its influence on superconductivity will also be discussed. Finally, point-contract spectroscopy on UPt 3 shows a strong anisotropy of Andreev reflection which, together with an unusual temperature and magnetic-field dependence, further supports the notion of unconventional superconductivity in this material. In particular, the different superconducting phases of UPt 3 have differentorder-parameter components.