Vortex Phase Dynamics in Yttrium Superhydride YH₆ at Megabar Pressures

A comprehensive study of vortex phases and vortex dynamicsispresented for a recently discovered high-temperature superconductorYH(6) with T (c)(onset) of 215 Kunder a pressure of 200 GPa. The thermal activation energy (U (0)) is derived within the framework of the thermallyactivated flux flow (TAFF) theory. The activation energy yields apower law dependence U (0) & PROP; H (& alpha;) on magnetic field with a possible crossoverat a field around 8-10 T. Furthermore, we have depicted thevortex phase transition from the vortex-glass to vortex-liquid stateaccording to the vortex-glass theory. Finally, vortex phase diagramis constructed for the first time for superhydrides. Very high estimatedvalues of flux flow barriers U (0)(H) = (1.5-7) x 10(4) K together withhigh crossover fields make YH6 a rather outstanding superconductoras compared to most cuprates and iron-based systems. The Ginzburgnumber for YH6 Gi = (3-7) x10(-3) indicates that thermal fluctuations are notso strong and cannot broaden superconducting transitions in weak magneticfields.