Evidence for Unconventional Superconductivity in Arsenic-Free Iron-Based Superconductor FeSe : A ^77Se-NMR Study

TL;DR

This study provides NMR evidence that the iron-based superconductor FeSe exhibits unconventional superconductivity, similar to arsenic-containing counterparts, suggesting the FeAs layer is not essential for this phenomenon.

Contribution

The paper demonstrates that FeSe, an arsenic-free superconductor, shows unconventional superconductivity through ^77Se-NMR, challenging the notion that FeAs layers are necessary.

Findings

^77Se-NMR reveals T^3 behavior of relaxation rate below Tc

Superconductivity in FeSe is unconventional, similar to arsenic-based materials

Fermi liquid behavior observed above Tc

Abstract

We report the results of $^{77}$Se--nuclear magnetic resonance (NMR) in $\alpha$-FeSe, which exhibits a similar crystal structure to the LaFeAsO$_{1-x}$F$_x$ superconductor and shows superconductivity at 8 K. The nuclear-spin lattice relaxation rate $1/T_1$ shows $T^3$ behavior below the superconducting transition temperature $T_c$ without a coherence peak. The $T_1T=$ const. behavior, indicative of the Fermi liquid state, can be seen in a wide temperature range above $T_c$. The superconductivity in $\alpha$-FeSe is also an unconventional one as well as LaFeAsO$_{1-x}$F$_x$ and related materials. The FeAs layer is not essential for the occurrence of the unconventional superconductivity.