El Hadi Sadki

Josephson vortex flow in Bi2Sr2CaCu2O8+y

Abstract In order to study the magnetic phase diagram of Josephson vortices, we have measured their flow resistance as a function of parallel magnetic field in Bi2Sr2CaCu2O8+y. Periodic oscillations are observed from about 6 kOe to larger than 70 kOe , which suggests the formation of Josephson vortex lattice as the ground state. However, depending on the applied current, we have found that Josephson vortex lattice in higher fields is not only triangular but also rectangular due to dynamical effects of Josephson vortex flow.

Ideal type II superconductivity of single-crystal niobium spheres solidified from the large undercooled state

We have developed an electrostatic levitation furnace for performing a containerless solidification process on superconductors. Spherical niobium is solidified from the large undercooled state at approximately around 400°C below the melting temperature. The morphologies show homogeneous cellular structures over the entire surface. X-ray Laue photographs indicate that the spherical niobium is composed of a single grain. Magnetization below the superconducting transition temperature shows perfect diamagnetism in the low magnetic field independent of whether loading is carried out under field cooling or zero-field cooling conditions. The field dependence of magnetization shows almost reversible behavior as that of an ideal type II superconductor. These results suggest that the spherical niobium formed from the large undercooled state in this study has a very small number of flux-pinning centers compared to that formed by conventional arc melting.

Dynamical behavior of Josephson vortices in Bi-2212

We have found periodic oscillations in the flux flow resistance of Josephson vortices along the c-axis of Bi-2212 single crystals. The resistance oscillates periodically with increasing parallel magnetic fields above about 6 kOe, independent of the magnitude of the field and temperature. The constant period of the oscillations and the dynamical behaviors of Josephson vortices suggest vortex states and a new application to the precise magnetic field sensors in Tesla order.

Niobium nitride/aluminum nitride superlattices

DC reactive magnetron sputtering has been used to prepare niobium nitride/aluminium nitride superconducting/insulator superlattices. Deposition conditions were optimized in order that multilayer fabrication could be achieved by simple computer control of the substrate positioning beneath each sputtering target.

Characterization of Josephson-vortex flow device as a magnetic sensor

We have found periodic oscillations in the Josephson-vortex flow resistance of the intrinsic Josephson junctions of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// single crystal under the parallel magnetic fields from a few kOe to more than 70 kOe. The oscillations indicate a precise and an absolute measurement at higher fields. To demonstrate the characteristics of the magnetic sensor, we have performed modulation measurements with small coils producing a few Oe in Tesla order magnetic fields and have studied details on the flow resistance in the magnetic field and temperature cycles. The results show a high performance as a magnetic sensor.

Vortex matter in NbN/AlN superconducting multilayers

Abstract The vortex matter (VM) in NbN/AlN multilayers (ML) is investigated by transport measurements in fields applied parallel and perpendicular to the layers. Similarly to HTS, the irreversibility line (IL) shifts to lower temperatures with increasing anisotropy. The resistivity of the higher anisotropy ML scales with the normal component of the field, suggesting the presence of a 2D VM above the IL. The activation energy of the less anisotropic sample scales with the number of the superconducting layers, in agreement with 3D VM. The resistivity and IV characteristic are compared with the Bose-glass theory.