Emergence of superconductivity in heavy-electron materials

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-12, Vol.111 (51), p.18178-18182
• Main Authors: Yang, Yi-feng, Pines, David
• Format: Article
• Language: English
• Subjects: Electrons; Glues; Materials; Parametric models; Particle physics; Phase transitions; Physical Sciences; Pressure dependence; Quantum physics; Quasiparticles; Specific heat; Superconductivity; Superconductors; Temperature effects; Transition temperature
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1422100112

Significance Although the pairing glue for the unconventional superconductivity found in heavy-electron materials has been identified as quantum critical spin fluctuations associated with their proximity to antiferromagnetic order, until now we have lacked a simple expression for their superconducting transition temperature, T c, that explains why T c changes with pressure, or varies from one material to another. The experiment-based expression proposed here parameterizes the effective frequency-dependent quasiparticle interactions in terms of their unusual normal-state properties; it provides a quantitative explanation of the measured pressure-induced variation in T c in the “hydrogen atoms” of unconventional superconductivity, CeCoIn ₅ and CeRhIn ₅, predicts a similar pressure variation for other heavy-electron quantum critical superconductors, and quantifies their variations in T c with a single parameter. Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy-electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at temperature T c that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors, where phonons provide the pairing glue. Here we propose such a model: a phenomenological BCS-like expression for T c in heavy-electron materials that is based on a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction and reflects the unusual properties of the heavy-electron normal state from which superconductivity emerges. We show that it provides a quantitative understanding of the pressure-induced variation of T c in the “hydrogen atoms” of unconventional superconductivity, CeCoIn ₅ and CeRhIn ₅, predicts scaling behavior and a dome-like structure for T c in all heavy-electron quantum critical superconductors, provides unexpected connections between members of this family, and quantifies their variations in T c with a single parameter.