Josephson-vortex Flow Resistance Research Articles

Magnetic phase diagram of Josephson vortices in strongly anisotropic superconductor Bi-2212

Magnetic phase diagram of Josephson vortices in strongly anisotropic superconductor Bi 2Sr 2CaCu 2O 8+δ has been studied by measuring the Josephson-vortex flow resistance. A triangular-lattice phase, in which periodic oscillations of the flow resistance have been observed, was found to start from about 6 kOe, independent of temperature. Although the triangular lattice phase exists over 7 T below 30 K, at higher temperatures the boundary to the others (glass phase) decreases with increasing temperature, and drops suddenly at 80 K. The flow resistance also decreases close to the boundary. These facts indicate that the thermal excitation of pancake vortex–antivortex pairs or missing a long-range order in the triangular lattice along the c-axis causes the reduction of the flow resistance. Furthermore, above the triangular lattice phase there finds some change in the flow resistance, which suggests the existence of a different kind of glass phases in the Josephson-vortex system.

Crossing vortex-lattices state probed by c-axis resistance in Bi2Sr2CaCu2O8+y

To investigate the properties of crossing lattices of pancake and Josephson vortices, we have measured the c-axis resistance Rc(H) as a function of field in Bi2Sr2CaCu2O8+y intrinsic Josephson junctions. When the sample is rotated in an applied field, Josephson-vortex flow resistance appears in the so-called lock-in state. Additionally, many equal steps of the resistance are observed in the range of fields where the crossing lattices are expected. The relationship between this phenomenon and crossing lattices is discussed.

Dynamical matching of Josephson vortex lattice with sample edge in layered high-Tc superconductors: origin of the periodic oscillation of flux flow resistance.

We numerically investigate Josephson vortex flow states in layered high-T(c) superconductors motivated by a recent experimental observation for accurate periodic magnetic field dependences of the Josephson vortex flow resistance over a wide range of magnetic field (0.5-4.0 T). We confirm in our mesoscale simulations that dynamical matching of Josephson vortex lattice with sample edge is responsible for the periodic dependence. The present simulations reveal that the Josephson vortex lattice flow speed is particularly suppressed when the moment of vortex entry matches that of vortex escape. Thus, the possible matching situations are taken into account and the observed periodicity is successfully explained.

Josephson vortex flow in Bi 2Sr 2CaCu 2O 8+ δ: Periodic oscillations of flow resistance

We have measured the Josephson vortex flow resistance with the current perpendicular to the Cu–O layers of Bi 2Sr 2CaCu 2O 8+ δ . It has been found that novel periodic oscillations appear in the flow resistance with sweeping the magnetic field parallel to the layers. The oscillations have been observed in a wide range of parallel fields larger than 6 kOe and only in a smaller current density than about 100 A/cm 2. The period of the oscillations corresponds to adding “one” flux quantum per “two” intrinsic Josephson junctions. These results suggest that the Josephson vortices form a triangular lattice as a ground state.