High-Tc superconductivity in FeSe at high pressure: Dominant hole carriers and enhanced spin fluctuations

TL;DR

This study reveals that high-pressure-induced high-Tc superconductivity in FeSe involves dominant hole carriers and enhanced spin fluctuations, aligning it more closely with iron pnictides than previously thought.

Contribution

It demonstrates the emergence of dominant hole carriers and increased spin fluctuations in high-pressure FeSe, suggesting a unified pairing mechanism with iron pnictides.

Findings

Hall resistivity changes sign from negative to positive with pressure

Enhanced interband spin fluctuations in high-Tc phase

Similarity between high-pressure FeSe and iron pnictides

Abstract

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc). However, high-Tc superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in the high-Tc phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-Tc superconducting phase transforms into high-Tc phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in striking contrast to other FeSe-derived high-Tc systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly enhanced interband spin fluctuations in the high-Tc phase. These results in FeSe highlight similarities with high-Tc phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.