Gap symmetry of the heavy fermion superconductor CeCu${}_2$Si${}_2$ at ambient pressure

Abstract

Recent observations of two nodeless gaps in superconducting CeCu${}_2$Si${}_2$ have raised intensive debates on its exact gap symmetry, while a satisfactory theoretical basis is still lacking. Here we propose a phenomenological approach to calculate the superconducting gap functions, taking into consideration both the realistic Fermi surface topology and the intra- and interband quantum critical scatterings. Our calculations yield a nodeless $s^{\pm }$-wave solution in the presence of strong interband pairing interaction, in good agreement with experiments. This provides a possible basis for understanding the superconducting gap symmetry of CeCu${}_2$Si${}_2$ at ambient pressure and indicates the potential importance of multiple Fermi surfaces and interband pairing interaction in understanding heavy fermion superconductivity.

arXiv comment7 pages, 5 figures

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