Superconductivity of 30.4 K and its Reemergence under Pressure in Fe1.11Se Synthesized via Ion-exchange and De-intercalation Reaction

TL;DR

This study reports the synthesis of a non-stoichiometric Fe1.11Se superconductor with a Tconset of 30.4 K, and explores its pressure-dependent superconducting behavior, revealing reemergence of superconductivity and magnetic order under pressure.

Contribution

It introduces a novel hydrothermal synthesis method for Fe1.11Se with excess interstitial Fe and investigates its unique pressure-induced superconducting and magnetic properties.

Findings

Superconducting Tconset of 30.4 K in Fe1.11Se achieved via ion-exchange.

Pressure causes a V-shaped Tconset evolution with reemergence of superconductivity.

Pressure induces possible magnetic order in the non-stoichiometric FeSe.

Abstract

Binary stoichiometry FeSe (s-FeSe) is a well-known parent of high-temperature unconventional superconductors owing to its charge-neutral layer, highly tunable structure and electronic properties, and rich interplays among multiple electronic phases. Yet the s-FeSe synthesized via high-temperature equilibrium reactions bears the notorious interstitial Fe,where merely 3% of them is sufficient to kill the superconductivity. Here, we successfully synthesized a new non-stoichiometric Fe1.11Se single crystal with a superconducting onset temperature (Tconset) of 30.4 K through a hydrothermal ion-exchange and de-intercalation route. 11% interstitial Fe ions exceed the equilibrium phase diagram limit. Intriguingly, under physical pressure, the Tconset of exhibits a "V"-shaped evolution with a minimum at 2-2.6 GPa, and then upturning into a second superconducting region, reminiscent of the behaviors in FeSe intercalates. Furthermore, a pressure-induced possible magnetic order, previously only observed in pressurized s-FeSe, shows up. These results offer fresh insights into the role of interstitial Fe in governing superconducting and transport properties under non-equilibrium synthesis and tuning strategies.