Pressure-induced high-temperature superconductivity retained without pressure in FeSe single crystals

What is it about?

To raise the superconducting-transition temperature (Tc) has been the driving force for the long-sustained effort in superconductivity research. Recent progress in hydrides with Tcs up to 287 K under pressure of 267 GPa has heralded a new era of room temperature superconductivity (RTS) with immense technological promise. Indeed, RTS will lift the temperature barrier for the ubiquitous application of superconductivity. Unfortunately, formidable pressure is required to attain such high Tcs. The most effective relief to this impasse is to remove the pressure needed while retaining the pressure-induced Tc without pressure. Here, we show such a possibility in the pure and doped high-temperature superconductor (HTS) FeSe by retaining, at ambient pressure via pressure quenching (PQ), its Tc up to 37 K (quadrupling that of a pristine FeSe at ambient) and other pressure-induced phases. We have also observed that some phases remain stable without pressure at up to 300 K and for at least 7 d. The observations are in qualitative agreement with our ab initio simulations using the solid-state nudged elastic band (SSNEB) method. We strongly believe that the PQ technique developed here can be adapted to the RTS hydrides and other materials of value with minimal effort.

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Photo by Daniel Abadia on Unsplash

Photo by Daniel Abadia on Unsplash

Why is it important?

As room temperature superconductivity (RTS) has been reported recently in hydrides at megabar pressures, the grand challenge in superconductivity research and development is no longer restricted to further increasing the superconducting transition temperature under extreme conditions and must now include concentrated efforts to lower, and better yet remove, the applied pressure required. This work addresses directly such a challenge by demonstrating our successful retention of pressure-enhanced and/or -induced superconducting phases and/or semiconducting phases without pressure in single crystals of superconducting FeSe and non-superconducting Cu-doped FeSe. The pressure-quenching technique developed in this work offers the possibility of future practical application and the unraveling of RTS recently detected in hydrides but only under high pressures.