Precise Pressure Dependence of the Superconducting Transition Temperature of FeSe: Resistivity and ^77Se--NMR Study

TL;DR

This study investigates how pressure affects the superconducting transition temperature of FeSe using resistivity and ^77Se--NMR measurements, revealing a maximum T_c of 21 K at 3.5 GPa and a close link between spin fluctuations and superconductivity.

Contribution

It provides the first detailed pressure dependence of T_c and 1/T_1 in FeSe, highlighting the role of spin fluctuations in its superconducting mechanism.

Findings

T_c increases with pressure, peaking at 21 K around 3.5 GPa.

A plateau in T_c and 1/T_1T suggests a link between spin fluctuations and superconductivity.

Bulk superconductivity confirmed by 1/T_1 measurements.

Abstract

We report the precise pressure dependence of FeSe from a resistivity measurement up to 4.15 GPa. Superconducting transition temperature (T_c) increases sensitively under pressure, but shows a plateau between 0.5-1.5 GPa. The maximum T_c, which is determined by zero resistance, is 21 K at approximately 3.5 GPa. The onset value reaches ~37 K at 4.15 GPa. We also measure the nuclear spin-lattice relaxation rate 1/T_1 under pressure using 77Se--NMR measurement. 1/T_1 shows that bulk superconductivity is realized in the zero-resistance state. The pressure dependence of 1/T_1T just above T_c shows a plateau as well as the pressure dependence of T_c, which gives clear evidence of the close relationship between 1/T_1T and T_c. Spin fluctuations are suggested to contribute to the mechanism of superconductivity.