Vortices in Dense Self-Assembled Hole Arrays

Vortex matter in presence of disorder Eli Zeldov Department of Condensed Matter Physics, Weizmann Institute of Science, Israel Several examples of the recent progress in comprehension of the equilibrium properties of vortex matter will be presented. Using microscopic Hall sensors and vortex shaking by in-plane ac field, a thermodynamic evidence of a first-order disorder-driven transition at intermediate temperatures in BSCCO crystals is found 1 . This transition displays a unique feature of inverse melting at which a disordered vortex phase transforms into an ordered lattice with increasing temperature. We conclude that the Bragg glass phase is destroyed through a unified first-order transition line that gradually changes its character from predominantly thermally-driven to predominantly disorderdriven at low temperatures. Transport investigations in NbSe2 crystals in Corbino geometry indicate that a firstorder disorder-driven transition is present also in low-Tc superconductors 2 . Using differential magneto-optical imaging we find that the thermally-driven melting transition is significantly broadened globally by material disorder, yet locally it remains a sharp first-order transition. Magnetic decoration studies show that a low concentration of columnar defects destroys the long-range order of the solid, forming ‘porous’ or amorphous structures. Nevertheless, it is found that the first-order transition is preserved and is shifted to higher temperatures 3 . [1] N. Avraham et al., Nature 411, 451 (2001). [2] Y. Paltiel et al., PRL 85, 3712 (2000). [3] S. S. Banerjee et al., PRL 90, 087004 (2003); M. Menghini et al., PRL 90, 147001 (2003).