Fully gapped $d$-wave superconductivity in CeCu${}_2$Si${}_2$

Abstract

The nature of the pairing symmetry of the first heavy fermion superconductor CeCu${}_2$Si${}_2$ has recently become the subject of controversy. While CeCu${}_2$Si${}_2$ was generally believed to be a $d$-wave superconductor, recent low temperature specific heat measurements showed evidence for fully gapped superconductivity, contrary to the nodal behavior inferred from earlier results. Here we report London penetration depth measurements, which also reveal fully gapped behavior at very low temperatures. To explain these seemingly conflicting results, we propose a fully gapped $d+d$ band-mixing pairing state for CeCu${}_2$Si${}_2$, which yields very good fits to both the superfluid density and specific heat, as well as accounting for a sign change of the superconducting order parameter, as previously concluded from inelastic neutron scattering results.

9 pages, 6 figures including Supplemental material. Published version in PNAS available online ahead of print at http://www.pnas.org/content/early/2018/05/07/1720291115

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• Magnetic Penetration Depth in Unconventional Superconductors
• Magnetically driven superconductivity in CeCu2Si2
• Nodeless pairing in superconducting copper-oxide monolayer films on Bi2Sr2CaCu2O8+δ
• Feedback spin resonance in superconducting CeCu${}_2$Si${}_2$ and CeCoIn${}_5$
• Orbital selectivity and emergent superconducting state from quasi-degenerate $s-$ and $d-$wave pairing channels in iron-based superconductors
• Orbital selective pairing and superconductivity in iron selenides
• Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu2Si2
• Emergent loop-nodal s${}_{\pm }$-wave superconductivity in CeCu${}_2$Si${}_2$: similarities to the iron-based superconductors
• Full-gap superconductivity robust against disorder in heavy-fermion CeCu2Si2
• Superconducting gap and vortex lattice of the heavy fermion compound CeCu_2Si_2
• Magnetic and superconducting properties on S-type single-crystal CeCu${}_2$Si${}_2$ probed by ${}^{63}$Cu nuclear magnetic resonance and nuclear quadrupole resonance
• Hidden Crossover Phenomena in Strongly Pauli Limited Multiband Superconductors ---Application to CeCu${}_2$Si${}_2$
• Effective pairing theory for strongly correlated d-wave superconductors

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