The structure of vortex arrays in high-temperature copper oxide superconductors in the presence of correlated defects and at elevated temperatures has been investigated using the magnetic decoration technique. Two-sided magnetic decoration experiments have been carried out on Bi_2Sr_2CaCu_2O_8(BSCCO) superconductors containing columnar defects either parallel or inclined at a 45 deg angle to the crystal c-axis. The positions of the individual columnar defect sites and vortices on the opposite sample sides were detemined by a chemical etching and decoration technique. When both the defect tracks and the appliced magnetic field are parallel to the c-axis, we have found that a fraction of the vortices tunnel between defect tracks as they traverse the sample. When the defect tracks are inclined at 45 deg from the c-axis while the extenal field is along the c-axis and below the matching field, the number of vortices tunneling between defect sites increases. In addition, Bitter decoration has been used to probe the structure of vortex arrays in BSCCO at temperatures up to 77 K. Comparison of the vortex lattice structure obtained at high temperature and 4.2 K shows the topological manifestation of thermal fluctuations at high temperature. Quantitative analysis of the configurations of vortices obtained from field-cooled and zero-field-cooled samples show the same sructure, and also suggest that the equilibrium state is a hexatic glass.
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