Pressure-induced high-Tc superconducting phase in FeSe: correlation between anion height and Tc

TL;DR

This study investigates how applying pressure affects the superconducting transition temperature (Tc) in FeSe, revealing a correlation between Tc and the height of selenium atoms, and suggesting anion height as a key factor in high-Tc superconductivity.

Contribution

It demonstrates a clear relationship between anion height and Tc under pressure, proposing a universal criterion for high-Tc in iron-based superconductors.

Findings

Maximum Tc of 30 K at 6 GPa in FeSe.

Linear resistivity dependence above Tc under pressure.

Correlation between Se height and Tc, applicable to other iron pnictides.

Abstract

In this study, we performed high-pressure electrical resistivity measurements of polycrystalline FeSe in the pressure range of 1-16.0 GPa at temperatures of 4-300 K. A precise evaluation of Tc from zero-resistivity temperatures revealed that Tc shows a slightly distorted dome-shaped curve, with maximum Tc (30 K) at 6 GPa, which is lower than a previously reported Tc value (~37 K). With the application of pressure, the temperature dependence of resistivity above Tc changes dramatically to a linear dependence; a non-Fermi-liquid-like "high-Tc" phase appears above 3 GPa. We found a striking correlation between Tc and the Se height: the lower the Se height, the more enhanced is Tc. Moreover, this relation is broadly applicable to other iron pnictides, strongly indicating that high-temperature superconductivity can appear only around the optimum anion height (~1.38A). On the basis of these results, we suggest that the anion height should be considered as a key determining factor of Tc of iron-based superconductors containing various anions.