Retaining Superconducting Phases Through Low-Temperature Pressure Quenching*

In the past 5 years the discovery of superhydride systems, with critical temperatures (T_cs) that approach and exceed room temperature, has pushed the field to new heights. Unfortunately, this novel room-temperature superconductivity (RTS) requires pressures in excess of 260 GPa, inhibiting their application outside academia. One of the greatest challenges remaining in the field of superconductivity is inducing and retaining RTS while lowering or removing the pressure. As a potential solution, we developed a low-temperature, pressure-quenching technique which we successfully used to retain superconducting phases in Bi and also FeSe and Cu_xFe_1-xSe. Quenching at 77 K and 4.2 K from pressures up to 26.6 GPa we retained Bi phases with varying T_cs corresponding to Bi III and V, as well as some ambiguous and/or novel phases. Similarly, we successfully retained superconducting phases with T_cs up to 37 K in FeSe and 27 K in Cu_xFe_1-xSe. Furthermore, the retained superconducting phases of these materials exhibited good stability at low temperature. In particular, Cu_xFe_1-xSe exhibited perfect stability for at least 7 days when quenched and kept at 77 K, retaining a T_c of ~25 K.