Abstract
Ce115 and related Ce compounds are particularly suited to detailed studies of the interplay of antiferromagnetic order, unconventional superconductivity and quantum criticality due to their availability as high quality single crystals and their tunability by chemistry, pressure and magnetic field. Neutron-scattering, NMR and angle-resolved thermodynamic measurements have deepened the understanding of this interplay. Very low temperature experiments in pure and lightly doped CeCoIn 5 have elaborated the FFLO-like magnetic state near the field-induced quantum-critical point. New, related superconducting materials have broadened the phase space for discovering underlying principles of heavy-fermion superconductivity and its relationship to nearby states. © 2012 The Physical Society of Japan.
Highlights
Superconductivity continues to fascinate the imagination even though it has been found in thousands of materials and in over half the elements. Irrespective of whether their superconducting transition temperature Tc is milliKelvin or tens of Kelvin, superconductivity in the vast majority of these can be understood within the weak coupling theory of Bardeen, Cooper, and Schrieffer (BCS) who showed that itinerant electrons form pairs due to an attractive interaction provided by phonons.1) Though this theory has had little success predicting where new examples might be found, its ability to account for a broad spectrum of experimental observations is very powerful
New opportunities to explore the relationship among magnetism, quantum criticality and unconventional superconductivity in heavy-fermion materials opened with the discovery of the ‘‘Ce115’’ family CeCoIn5,11) CeRhIn5,12) and CeIrIn5.13) were CeCoIn5 and CeIrIn5 the first Ce-based heavy-fermion systems since CeCu2Si2 to exhibit superconductivity at atmospheric pressure, the transition temperature of pressure-induced superconductivity in the isostructural, antiferromagnetic member CeRhIn5 was 2.3 K, much higher than prior examples
In conventional s-wave superconductors, Abrikosov and Gor’kov showed that very small amounts of magnetic impurities break timereversal symmetry of the phase-coherent superconducting condensate and globally suppress Tc rapidly to zero; whereas, in d-wave superconductors non-magnetic impurities should behave as magnetic impurities in s-wave systems.57) A strikingly different interpretation has come from a thermodynamic analysis of the superconducting condensation energy of CeCoIn5 doped with non-magnetic impurities, such as Yb2þ, La3þ, Y3þ, and Th4þ.58) This study suggests that impurities create an electronically inhomogeneous superconducting state, effectively ‘‘digging a hole’’ in the condensate and forming a normal state volume that grows precisely at the expense of a decreasing superconducting volume
Summary
(Received February 18, 2011; accepted April 25, 2011; published online December 26, 2011) Ce115 and related Ce compounds are suited to detailed studies of the interplay of antiferromagnetic order, unconventional superconductivity and quantum criticality due to their availability as high quality single crystals and their tunability by chemistry, pressure and magnetic field. Neutron-scattering, NMR and angle-resolved thermodynamic measurements have deepened the understanding of this interplay. Very low temperature experiments in pure and lightly doped CeCoIn5 have elaborated the FFLO-like magnetic state near the field-induced quantum-critical point. New, related superconducting materials have broadened the phase space for discovering underlying principles of heavy-fermion superconductivity and its relationship to nearby states
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