Retention of high-pressure-induced superconducting and non-superconducting phases in non-superconducting and high-temperature-superconducting solids at ambient

To raise the Tc has been one of the main driving forces in the extensive research on high-temperature superconductivity of the past more than three decades. Numerous Tc-records have been set for different compound systems, i.e., 164 K for Hg1223 under 31 GPa by Chu et al. in 1994, 203 K for H3S under 155 GPa by Eremets et al. in 2015, 260 K for LaH10 under 190 GPa by Hemley et al. in 2019, and 287 K in a C-S-H hydride under 267 GPa by Dias et al. in 2020. Indeed, room-temperature superconductivity is within reach. Unfortunately, extreme pressures are required, raising a formidable hurdle to the wonderland of room-temperature superconductivity for scientific research and technological applications. To remove the obstacle, we have investigated means to retain these high-pressure-induced phases at ambient without pressure. By taking advantage of the energy barriers between phases through a pressure-quenching (PQ) process following a specific thermodynamic path at different temperatures, we have demonstrated the workability of the approach. We shall report our success in retaining at ambient the following pressure-induced phases: superconducting (sc) phases II at ~5-20 GPa and IV at ~22-62 GPa in non-sc Sb I single crystals; sc phases III at ~2.4-7 GPa and V above ~ 7 GPa in non-sc Bi I single crystals; sc tetragonal FeSe at ~2-7.5 GPa and non-sc hexagonal FeSe above ~8 GPa in sc orthogonal FeSe single crystals; and sc tetragonal Cu-doped FeSe at ~4-6 GPa in non-sc orthogonal Cu-doped FeSe single crystals. The thermal stability of each of these phases has also been determined. For example, the superconducting phase in FeSe with a Tc of ~ 38 K (quadrupling the Tc at ambient before PQ) has been retained without pressure after PQ at ~ 4 GPa and 4.2 K and the PQ phase is stable up to ~ 200 K.
The work performed at the Texas Center of Superconductivity at the University of Houston is supported by US Air Force Office of Scientific Research Grants FA9550-15-1-0236 and FA9550-20-1-0068, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston. The FeSe and Cu-doped FeSe single-crystal growth work at Rice University is supported by the US Department of Energy, Basic Energy Sciences, under Contract DE-SC0012311 (P.D.).