The role of 245 phase in alkaline iron selenide superconductors revealed by high pressure studies

TL;DR

This study investigates how high pressure affects the phase transitions in alkaline iron selenide superconductors, revealing the suppression of insulating phases and the emergence of an orbital selective Mott phase linked to superconductivity.

Contribution

It provides new insights into the pressure-induced phase transitions and the role of the orbital selective Mott phase in the superconducting mechanism of iron selenides.

Findings

Pressure suppresses vacancy order and insulating phase around 8 GPa.

A second transition occurs near 18 GPa.

Intermediate metallic phase exhibits orbital selective Mott behavior.

Abstract

Here we show that a pressure of about 8 GPa suppresses both the vacancy order and the insulating phase, and a further increase of the pressure to about 18 GPa induces a second transition or crossover. No superconductivity has been found in compressed insulating 245 phase. The metallic phase in the intermediate pressure range has a distinct behavior in the transport property, which is also observed in the superconducting sample. We interpret this intermediate metal as an orbital selective Mott phase (OSMP). Our results suggest that the OSMP provides the physical pathway connecting the insulating and superconducting phases of these iron selenide materials.