Superconductivity at 36 K in beta-Fe1.01Se with the compression of the interlayer separation under pressure

TL;DR

This study demonstrates that applying pressure significantly enhances the superconducting transition temperature of beta-Fe1.01Se, linked to structural changes and layer separation collapse, revealing unconventional superconductivity mechanisms.

Contribution

It provides new insights into pressure-induced superconductivity and structural transitions in beta-Fe1.01Se, emphasizing the role of electron correlations in its behavior.

Findings

Tc increases from 8.5 to 36.7 K under 8.9 GPa pressure

Layer separation collapse correlates with Tc rise

High-pressure phase becomes non-magnetic, insulating

Abstract

In this letter, we report that the superconductivity transition temperature in beta-Fe1.01Se increases from 8.5 to 36.7 K under applied pressure of 8.9 GPa. It then decreases at higher pressure. A dramatic change in volume is observed at the same time Tc rises, due to a collapse of the separation between the Fe2Se2 layers. A clear transition to a linear resistivity normal state is seen on cooling at all pressures. No static magnetic ordering is observed for the whole p-T phase diagram. We also report that at higher pressure (starting around 7 GPa and completed at 38 GPa), Fe1.01Se transforms to a hexagonal NiAs-type structure and displays non-magnetic, insulating behavior. The inclusion of electron correlation in band structure caculations is necessary to describe this behavior, signifying that such correlations are important in this chemical system. Our results strongly support unconventional superconductivity in beta-Fe1.01Se.