77Se NMR study of pairing symmetry and spin dynamics in KyFe2-xSe2

TL;DR

This study uses 77Se NMR to investigate the pairing symmetry and spin dynamics in the superconductor KyFe2-xSe2, revealing singlet pairing and Fermi-liquid behavior, which constrains theories of its high-temperature superconductivity.

Contribution

First NMR investigation of KyFe2-xSe2 revealing pairing symmetry and spin dynamics, providing constraints on superconductivity mechanisms.

Findings

Sharp drop in Knight shift below Tc indicating singlet pairing

Fermi-liquid behavior above Tc from relaxation data

Experimental constraints on theoretical models of high-Tc superconductivity

Abstract

We present a 77Se NMR study of the newly discovered iron selenide superconductor KyFe2-xSe2, in which Tc = 32 K. Below Tc, the Knight shift 77K drops sharply with temperature, providing strong evidence for singlet pairing. Above Tc, Korringa-type relaxation indicates Fermi-liquid behavior. Our experimental results set strict constraints on the nature of possible theories for the mechanism of high-Tc superconductivity in this iron selenide system.