Retention of Enhanced and Induced Superconductivity at Ambient Pressure Through High-Pressure Quenching



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In the past eight years impressively high superconducting critical temperatures (Tcs) have been reported in numerous materials. Among these include instances of anomalously high Tcs that approach, and in some contested reports, meet and exceed room temperature (RT), pushing the field to new heights. Unfortunately, achieving such impressive critical temperatures requires ultra-high external pressures, rendering them unviable for commercial use. Therefore, one of the most significant challenges remaining in the field of superconductivity is to retain the high Tc phases induced by pressure while lowering or removing it completely. We have therefore employed a pressure quenching technique to retain high-pressure-induced/-enhanced superconducting phases in Bi, FeSe, and CuxFe1.01-xSe at ambient pressure. Pressure quenching bismuth at 77 K and 4.2 K from pressures up to 26.6 GPa successfully produced metastable superconducting phases with varying Tcs from ∼ 5 K up to a new record of 9 K. By changing the pressure quenching parameters, different metastable phases could be targeted, namely Bi-III with a Tc around 7 K and Bi-V with a Tc > 8 K. Temporal stability testing and thermal cycling revealed a lower temperature limit below ∼ 60 K and an upper temperature limit of 120 K – 150 K in metastable bismuth. Pressure quenches performed on FeSe and CuxFe1.01-xSe near the superconducting dome resulted in metastable phases with maximum Tcs of 37 K and 25 K, respectively. Thermal cycling of FeSe and CuxFe1.01-xSe showed a similar lower temperature limit for temperatures up to ∼ 120 K and an upper temperature limit around 175 K for CuxFe1.01-xSe. Annealing metastable FeSe to room temperature produced Tcs from 15 K – 24 K. Notably, a non-superconducting hexagonal phase retained in FeSe was slowly annealed to room temperature for a few days resulting in a superconducting phase near the dome peak. Lastly, a temporal stability test of metastable CuxFe1.01-xSe was conducted which showed perfect phase stability for 7 days when kept below 50 K. Overall, these results demonstrate the potential this technique has in targeting desirable superconducting phases induced or enhanced by pressure and retaining them in a metastable state at ambient pressure.



superconductivity, superconductor, FeSe, CuxFe1.01-xSe, Bi, Bismuth, high pressure,low temperature, pressure quench, critical temperature, metastable


Portions of this document appear in: L. Deng, T. Bontke, R. Dahal, Y. Xie, B. Gao, et al. Pressure-induced high-temperature superconductivity retained without pressure in FeSe single crystals. Proceedings of the National Academy of Sciences, 118(28), 2021.