Search

A comprehensive study of vortex phases and vortex dynamics is presented for a recently discovered high-temperature superconductor YH 6 with T c (onset) of 215 K under a pressure of 200 GPa. The thermal activation energy ( U 0 ) is derived within the framework of the thermally activated flux flow (TAFF) theory. The activation energy yields a power law dependence U 0 ∝ H α 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 U 0 ( H ) = (1.5-7) × 10 4 K together with high crossover fields make 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.

In pnictide RbEuFe 4 As 4 , superconductivity sets in at 36 K and coexists, below 15-19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-terminated and small Eu-terminated terraces, both manifesting 1 × 2 and 2 × 2 reconstructions. On 2 × 2 surfaces, a hidden electronic order with a period ∼5 nm was discovered. A superconducting gap of ∼7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated ∼1.8 eV below the Fermi level and thus do not contribute directly to Cooper pair formation.