The nature of the pairing symmetry of the first heavy fermion superconductor CeCu2Si2 has recently become the subject of controversy. While CeCu2Si2 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 CeCu2Si2, 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.
@article{arxiv.1605.04786,
title = {Fully gapped $d$-wave superconductivity in CeCu$_2$Si$_2$},
author = {G. M. Pang and M. Smidman and J. L. Zhang and L. Jiao and Z. F. Weng and E. M. Nica and Y. Chen and W. B. Jiang and Y. J. Zhang and W. Xie and H. S. Jeevan and H. Lee and P. Gegenwart and F. Steglich and Q. Si and H. Q. Yuan},
journal= {arXiv preprint arXiv:1605.04786},
year = {2018}
}
Comments
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