Vortex Lattice Melting into Disentangled Liquid Followed by the 3D-2D Decoupling Transition in YBa_2Cu_4O_8 Single Crystals

TL;DR

This study investigates vortex lattice melting and decoupling transitions in high-quality YBa_2Cu_4O_8 single crystals, revealing a two-stage process with distinct flux flow regimes and a transition from a disentangled liquid to a 3D-2D decoupled state.

Contribution

It provides experimental evidence for vortex lattice melting into a disentangled liquid followed by a 3D-2D decoupling transition in YBa_2Cu_4O_8 crystals, supported by resistance measurements and theoretical analysis.

Findings

Observation of sharp resistance drop indicating vortex lattice melting.

Identification of two thermally activated flux flow regions separated by a crossover line.

Evidence for a transition from a disentangled vortex liquid to a 3D-2D decoupled state.

Abstract

A sharp resistance drop associated with vortex lattice melting was observed in high quality YBa_2Cu_4O_8 single crystals. The melting line is well described well by the anisotropic GL theory. Two thermally activated flux flow regions, which were separated by a crossover line B_cr=1406.5(1-T/T_c)/T (T_c=79.0 K, B_cr in T), were observed in the vortex liquid phase. Activation energy for each region was obtained and the corresponding dissipation mechanism was discussed. Our results suggest that the vortex lattice in YBa_2Cu_4O_8 single crystal melts into disentangled liquid, which then undergoes a 3D-2D decoupling transition.