Vortex phase dynamics in yttrium superhydride YH${}_6$ at megabar pressures

Abstract

A comprehensive study of the vortex phases and vortex dynamics is presented for a recently discovered high-temperature superconductor YH${}_6$ with T${}_C$ (onset) of 215 K under pressure of 200 GPa.Thermal activation energy (U${}_0$) is derived in the framework of thermally activated flux flow (TAFF) theory. The activation energy yields a power law dependence U${}_0$ $\propto$ H${}^{\alpha }$ on magnetic field with a possible crossover at a field around 8-10 Tesla. Furthermore, we have depicted the vortex phase transition from vortex-glass to vortex-liquid state according to the vortex-glass theory. Finally, vortex phase diagram is constructed for the first time for superhydrides. Very high estimated values of flux flow barriers U${}_0$(H) = 1.5-7*10${}^4$ K together with high crossover fields makes YH${}_6$ a rather outstanding superconductor as compared to most cuprates and iron-based systems. The Ginzburg number for YH${}_6$ Gi = 3-7*10${}^{-3}$ indicates that thermal fluctuations are not so strong and cannot broaden superconducting transitions in weak magnetic fields.

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