Vortex States in Strongly Anisotropic HTSC in Parallel Magnetic Field

High Tc superconductors (HTSCs) for the application of magnets and cables are usually used in a magnetic field parallel to the superconducting layers, using the intrinsic pinning of vortices in the layered structures. However, vortex states in the parallel field have not been well understood in strongly anisotropic superconductors. We have studied the vortex states by measuring the flow resistivity of Josephson vortices (JVs). From the measurements, we can determine the 3D-ordered phase of JVs, which means that JVs are well ordered and are considered not to influence the dissipation of the superconducting state. However, by the R-T measurements, we have found the excitation of pancake vortex/anti-vortex pairs to reduce the flow resistance. This limits the application of HTSC materials in the parallel magnetic fields.