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TT: Tiefe Temperaturen

TT 7: Superconductivity & Solids At Low Temperature - Poster Session

TT 7.62: Poster

Montag, 27. März 2006, 14:00–17:45, P1

Evidences for Flux Line Termination Inside of a Highly Anisotropic Superconductor: A Magnetic Force Microscopy Study — •Ung Hwan Pi¹, Alexander Schwarz¹, Marcus Liebmann², Zheong Gu Khim³, Dong Ho Kim⁴, and Roland Wiesendanger¹ — ¹University of Hamburg, IAP, Jungiusstr. 11, 20355 Hamburg — ²Present Address: RWTH Aachen, Department of Physics, 52056 Aachen — ³School of Physics, SNU, Seoul 151-742, South Korea — ⁴Dept. of Physics, Yeungnam University, Kyungsan, South Korea

In highly anisotropic layered superconductors like Bi₂Sr₂CaCu₂O_8+δ, the Josephson coupling between each layer is so weak that the phase coherence in c-direction is negligible and the termination of the flux line inside the sample is not forbidden by topology of the phase. Mints et al.[1] have reported in a theoretical study that the termination of the flux line inside the sample is energetically favorable for small enough samples. Our magnetic force microscopy study performed on the Bi₂Sr₂CaCu₂O_8+δ single crystal showed some evidences supporting this prediction. Since all flux lines have single flux quantum, they should exhibit the same contrast. However, we could observe a somewhat weaker contrast at several flux lines near an antiphase boundary. Two weak-contrast flux lines sometimes merged into one flux line with a stronger contrast. These weak magnetic contrasts are possible candidates for flux lines terminating beneath the sample surface.

[1] G. Mints et al. Phys. Rev. B 61, 1623 (2000).