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TT: Tiefe Temperaturen

TT 33: Superconductivity: Vortex Dynamics, Vortex Phases, Pinning

TT 33.9: Vortrag

Freitag, 31. März 2006, 12:15–12:30, HSZ 304

How the Flux Line Lattice in the Anisotropic High-T_c Superconductor Bi₂Sr₂CaCu₂O_8+δ Melts: A Magnetic Force Microscopy study — •Alexander Schwarz¹, Marcus Liebmann², Ung Hwan Pi¹, and Roland Wiesendanger¹ — ¹University of Hamburg, IAP, Jungiusstr. 11, 20355 Hamburg — ²Present Address: RWTH Aachen, Department of Physics, 52056 Aachen

The behavior of a trigonal flux line lattice corresponding to a flux density of about 3.5 mT was investigated in a Bi₂Sr₂CaCu₂O_8+δ single crystal upon increasing the temperature stepwise from 5.1 K towards T_c. In this highly anisotropic material flux lines consist of relative weakly bound pancake vortices confined to the copper oxide planes. Magnetic force microscopy images recorded with single flux line resolution revealed a temperature dependence of the regularity of the long-range order and the apparent flux-line size. Both observations can be explained by the interplay between the temperature dependence of the London penetration depth, collective pinning and subsequent depinning above 30 K, thermal motion of the vortices and lateral dragging by the force sensor itself. At the highest temperature the typical flux line contrast composed of a coherent alignment of pancake vortices along the crystal c-axis disappeared. Instead, a liquid-like behavior of individual pancakes can be observed.