Unconventional multiband superconductivity with nodes in single-crystalline SrFe2(As_0.65P_0.35)2 as seen via 31P-NMR and specific heat

TL;DR

This study investigates the unconventional multiband superconductivity with nodal gaps in SrFe2(As0.65P0.35)2 using 31P-NMR and specific heat measurements, revealing antiferromagnetic correlations and gap structures affecting superconducting properties.

Contribution

It provides new insights into the multiband superconducting gap structure with nodes and the interplay of large full gaps and small nodal gaps in Fe-based superconductors.

Findings

Revealed antiferromagnetic correlations in the normal state.

Identified nodal gap structure causing gapless quasiparticle excitations.

Suggested large full gaps coexist with small nodal gaps in the superconductor.

Abstract

We report 31P-NMR and specific heat measurements on an iron (Fe)-based superconductor SrFe2(As0.65P0.35)2 with Tc=26 K, which have revealed the development of antiferromagnetic correlations in the normal state and the unconventional superconductivity(SC) with nodal gap dominated by the gapless low-lying quasiparticle excitations. The results are consistently argued with an unconventional multiband SC state with the gap-size ratio of different bands being significantly large; the large full gaps in s\pm-wave state keep Tc high, whereas a small gap with a nodal-structure causes gapless feature under magnetic field. The present results will develop an insight into the strong material dependence of SC-gap structure in Fe-based superconductors.