The Retention of High-Pressure-Induced High-Tc Superconductivity at Ambient Pressure

This short review article is dedicated to Prof. Müller on the occasion of his 95th birthday. In the past few years, several reports of high superconducting transition temperatures (Tcs) above 200 K in hydrides under pressure above 150 GPa have appeared. The ultrahigh pressures needed to achieve the high-Tc superconducting state render these marvelous compounds difficult to be thoroughly studied using the well-known material characterization tools developed and employed for the study of the cuprate high-temperature superconductors at ambient pressure, impeding our understanding of the high-pressure-induced very high Tc state for science, and making the high-pressure-induced phases impractical for applications. To provide a relief to this impasse, we have developed a pressure-quench process (PQP) and have demonstrated it successfully in stabilizing at ambient pressure the high-pressure-induced superconducting phases and other phases in the non-superconducting element Sb, the binary superconducting compound FeSe, and the non-superconducting compound Cu-doped FeSe. It is not inconceivable that the PQP may be adapted for cuprates and hydrides with high-pressure-induced high Tc for science and technology. Our recent results and both the opportunities and challenges will be discussed.