Quasi-static and dynamic order-disorder transition in presence of strong pinning

TL;DR

This study investigates vortex dynamics in a YBa2Cu3O7 crystal, revealing how critical currents vary with magnetic field and demonstrating the role of dynamic ordering and transverse barriers in vortex state transitions.

Contribution

It provides experimental evidence of the difference between static and dynamic order-disorder transitions in vortex matter and explains the influence of transverse barriers on vortex displacements.

Findings

Critical currents vary non-monotonically with magnetic field.

Minimum in dynamic critical current occurs at higher fields than static transition.

Finite transverse barriers sustain the disordered vortex state during motion.

Abstract

We present the results of an experimental study of vortex dynamics in non-twinned $YBa_2Cu_3O_{6,87}$ crystal. It is found that critical currents $J_c$ and $J_{c,dyn}$, which correspond to the pinning force in the thermal creep and flux flow mode, respectively, non-monotonically vary with the magnetic field. However, the minimum in the $J_{c,dyn}(H)$ dependence is observed in higher fields, compared with the minimum position $H_{OD}$ in the $J_c(H)$ dependence. Considering that the field $H_{OD}$ corresponds to the static order-disorder transition, this difference is explained by partial dynamic ordering of the vortex solid. It is concluded that finite transverse barriers guarantee finite density of transverse displacements of vortex lines $u_t\simeq c_La_0$ suitable for preservation of the disordered state of the moving vortex solid.