Anomalous behavior of the flux line lattice of vibrating high-Tcsuperconductors at 30 K in magnetic fields parallel to theCuO2planes

Abstract

We have measured the energy dissipation and pinning of the flux line lattice (FLL) of vibrating high-${\mathit{T}}_{\mathit{c}}$ superconducting crystals as a function of temperature, magnetic field, and angle θ between field and ${\mathrm{CuO}}_2$ planes. For ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ and oxygen-deficient (${\mathrm{Y}}_{0.94}$ ${\mathrm{Gd}}_{0.06}$)${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.83}$ superconductors and for θ∼0° we observed an anomalous depinning of the FLL at ∼30 K. This anomaly cannot be explained by a thermally activated depinning mechanism and suggests the existence of a phase transition of the FLL.