Imaging the effect of drive on the low-field vortex melting phenomenon in a Ba0.6K0.4Fe2As2 single crystal

Abstract

Self-field imaging of current distribution in the $\mathrm{B}{\mathrm{a}}_{0.6}{\mathrm{K}}_{0.4}\mathrm{F}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ superconductor is used to study the effect of drive on the low-field vortex solid to liquid melting phase transformation. At low fields, the current-induced drive on the vortices aids in thermally destabilizing the low field glassy vortex (solid) phase, thereby shifting the low-field melting phase boundary. We show that the current-induced drive shifts solid-liquid boundaries and prepones the vortex melting phenomenon compared to the equilibrium situation. The analysis shows that, for currents above 50 mA, Joule heating effects shift the melting line whereas, below 50 mA, an effective temperature concept for the driven system viz., a drive-dependent shaking temperature, explains the shift. The observation of a transformation from inhomogeneous to homogeneous current flow in the sample at low fields as a function of the driving force is reconciled via an inverse dependence of the shaking temperature on vortex velocity.