First-order vortex phase transition in Bi2Sr2CaCu2Oy single crystals with different carrier concentrations studied by resistivity measurements - art.no. 064520

The first-order vortex phase transition (FOT) in Bi2Sr2CaCu2Oy single cryst als with different carrier concentrations was investigated by measuring the in-plane resistivity (rho (ab)) under a magnetic field applied parallel to the crystallographic c-axis direction. With a decrease in the temperature, rho (ab) dropped sharply at the FOT temperature when the applied field was smaller than the second-peak field (H-pk) that was determined by measuring the magnetic hysteresis curves at 25-30 K, while no such abrupt change was observed when the applied field was larger than H-pk. The temperature rang e where the FOT was observed was approximately between 0.6 to 0.95 in the s cale of the reduced temperature (t =T/T-c) for all crystals. The first-orde r transition field (H-t) as a function of t shifted to higher fields as the carrier concentration of the crystal increased, which can be well scaled b y the electromagnetic anisotropy factor (gamma). Irrespective of the carrie r doping level, the temperature dependence of H-t is experimentally express ed better by H-t(proportional to) (t(-1)-t) rather than the functional form proposed by the conventional decoupling theory of the vortex lattice [H-t( proportional to)(t(-1)-1)]. This experimental formula can be accounted for by the decoupling theory if the temperature dependence of the magnetic pene tration depth is assumed to scale as lambda (-2)proportional to (1-t(2)).