Berlin 2018 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 22: Superconductivity: Topological Defects in Superconductors and Magnets (joint session TT/MA)

TT 22.8: Vortrag

Montag, 12. März 2018, 17:00–17:15, HFT-FT 101

Unusual critical state and vortex commensurability in cuprate superconductors with regular topological defects — •Wolfgang Lang¹, Georg Zechner¹, Kristijan L. Mletschnig¹, Florian Jausner¹, Meirzhan Dosmailov², Marius A. Bodea², and Johannes D. Pedarnig² — ¹University of Vienna, Faculty of Physics, Wien, Austria — ²Johannes-Kepler-University Linz, Institute of Applied Physics, Linz, Austria

The interaction of vortices with artificial defects in a superconductor is a vibrant topic in experimental and theoretical research, but also important for its prospects of technical applications. The advantage of a higher operation temperature in YBa₂Cu₃O_7−δ (YBCO) is opposed by the demand for advanced nanopatterning methods. To this end, YBCO thin films are irradiated with He⁺ ions by shadow projection through a Si stencil mask to create a square array of columnar defect regions of 180 nm diameter and 300 nm lattice constant. Peaks of the critical current as a function of the applied magnetic field reveal the commensurate trapping of vortices in domains near the edges of the sample. Upon ramping an external magnetic field, an unconventional critical state emerges that is characterized by a pronounced hysteresis and different positions of the critical current peaks in virgin and field-saturated down-sweep curves, respectively. Interestingly, the distances of the various peaks in a sweep remain constant and correspond exactly to the matching field. The observations are interpreted as a nonuniform, terrace-like critical state, in which individual domains are occupied by a fixed number of vortices per pinning site.