Emergent Loop-Nodal ${s}_{\ifmmode\pm\else\textpm\fi{}}$-Wave Superconductivity in ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$: Similarities to the Iron-Based Superconductors

Emergent Loop-Nodal $s_{\pm}$ -Wave Superconductivity in ${CeCu}_{2} {Si}_{2}$ : Similarities to the Iron-Based Superconductors

Hiroaki Ikeda, Michi-To Suzuki, and Ryotaro Arita

Phys. Rev. Lett. 114, 147003 – Published 7 April 2015

Abstract

Heavy-fermion superconductors are prime candidates for novel electron-pairing states due to the spin-orbital coupled degrees of freedom and electron correlations. Superconductivity in ${CeCu}_{2} {Si}_{2}$ discovered in 1979, which is a prototype of unconventional (non-BCS) superconductors in strongly correlated electron systems, still remains unsolved. Here we provide the first report of superconductivity based on the advanced first-principles theoretical approach. We find that the promising candidate is an $s_{\pm}$ -wave state with loop-shaped nodes on the Fermi surface, different from the widely expected line-nodal $d$ -wave state. The dominant pairing glue is magnetic but high-rank octupole fluctuations. This system shares the importance of multiorbital degrees of freedom with the iron-based superconductors. Our findings reveal not only the long-standing puzzle in this material, but also urge us to reconsider the pairing states and mechanisms in all heavy-fermion superconductors.