Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs

TL;DR

This study reveals that PrO0.89F0.11FeAs exhibits spin-singlet superconductivity with multiple energy gaps and potential nodes, providing new insights into high-temperature superconductivity mechanisms.

Contribution

It demonstrates the presence of multiple gaps and spin-singlet pairing in PrO0.89F0.11FeAs, a novel finding among high-Tc superconductors.

Findings

Spin-singlet pairing confirmed in PrO0.89F0.11FeAs.

Two energy gaps observed below Tc.

Evidence suggests the existence of nodes in the superconducting gap.

Abstract

Since the discovery of high transition-temperature (Tc) superconductivity in copper oxides two decades ago, continuous efforts have been devoted to searching for similar phenomenon in other compounds. With the exception of MgB2 (Tc =39 K), however, Tc is generally far lower than desired. Recently, breakthrough has been made in a new class of oxypnictide compounds. Following the initial discovery of superconductivity in LaO1-x FxFeAs (Tc =26 K), Tc onset has been raised to 55 K in ReO1-xFxFeAs (Re: Ce, Pr, Nd, Sm). Meanwhile, unravelling the nature of the energy associated with the formation of current-carrying pairs (Cooper pairs), referred to as the superconducting energy gap, is the first and vital step towards understanding why the superconductivity occurs at such high temperature and is also important for finding superconductors with still higher Tc. Here we show that, on the basis of the nuclear magnetic resonance (NMR) measurements in PrO0.89F0.11FeAs (Tc =45 K), the Cooper pair is in the spin-singlet state (two spins are anti-paralleled), with two energy gaps opening below Tc. The results strongly suggest the existence of nodes (zeros) in the gap. None of superconductors known to date has such unique gap features, although copper-oxides and MgB2 share part of them.