Vortex Phases in Mesoscopic Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ Single Crystals in Magnetic Fields Near \textit{ab}-plane

In order to study the vortex matter in the layered superconductors in magnetic fields parallel to the \textit{ab}-plane, we performed the in-plane resistivity and the $c$-axis resistivity measurements on the bulk and mesoscopic Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ single crystals. In the bulk samples, a boundary between the strong pinning phase and the weak pinning vortex phase was found at about 3$^{o}$ away from the \textit{ab}-plane, indicating possible crossover from the vortex chain + lattice phase into tilted (vortex chain) phase. The vortex phase in the parallel magnetic fields, exhibited a strongly non-Ohmic behavior, indicating the possible two-stage melting phase transition. It was found that the vortex lock-in transition in mesocopic crystals, becomes considerably broad in high magnetic fields, while exhibiting the sharp features in low magnetic field region. The first penetration field of vortex pancakes demonstrates a nontrivial field dependence.