Vortex Phase Dynamics in Yttrium Superhydride YH6 at Megabar Pressures.

ABSTRACT

A comprehensive study of vortex phases and vortex dynamics is presented for a recently discovered high-temperature superconductor YH6 with Tc(onset) of 215 K under a pressure of 200 GPa. The thermal activation energy (U0) is derived within the framework of the thermally activated flux flow (TAFF) theory. The activation energy yields a power law dependence U0 ∝ Hα on magnetic field with a possible crossover at a field around 8-10 T. Furthermore, we have depicted the vortex phase transition from the 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 U0(H) = (1.5-7) × 104 K together with high crossover fields make YH6 a rather outstanding superconductor as compared to most cuprates and iron-based systems. The Ginzburg number for YH6 Gi = (3-7) × 10-3 indicates that thermal fluctuations are not so strong and cannot broaden superconducting transitions in weak magnetic fields.