Simultaneous resistivity onset and first-order vortex-lattice phase transition in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$Ca${\mathrm{Cu}}_2$${\mathrm{O}}_8$

Simultaneous measurements of resistivity and local magnetization using microscopic Hall sensors were carried out on ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$Ca${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$ crystals as a function of applied field and temperature. The resistivity onset is found to occur concurrently with the first-order vortex-lattice phase transition, determined by the equilibrium magnetization step. This behavior strongly suggests that the vortex lattice melts at the phase transition. The apparently reversible magnetization below the transition is ascribed to substantial flux creep.