VORTEX LOCALIZATION AND BOSE GLASS STATE IN HIGH-TEMPERATURE SUPERCONDUCTORS

The manifestations of vortex localization at columnar defects in the t ransport properties of Tl-cuprates have been studied in detail. Such d efects are produced by irradiation of the materials with 250 similar t o 300 MeV ions of silver. The defects are essentially tracks of amorph ised material and can be imaged with high resolution transmission elec tron microscopy and atomic force microscopy techniques. A large shift of the onset of nux now resistivity and irreversibility line to higher temperatures occurs due to vortex localization at these defects. The angular dependence of the nux now resistivity shows evolution of a flu x lock-in state as the external field is brought into alignment with t he columnar defects. This observation provides compalling evidence for non-zero line tension of vortices in these highly layered compounds. The temperature dependence of flux flow resistivity and non-linear dis sipation at perfect alignment are consistent with the Bose glass ideas for the mixed state. Measurements of the critical current density sho w that the pinning force of the columnar defects is stronger than the pinning force due to the intrinsic interlayer variation of the order p arameter. In contrast to these observations, samples with: proton-irra diation-induced point defects show marginal pinning even at T < < T-c.