Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 21: Superconductivity: Poster Session

TT 21.31: Poster

Monday, March 16, 2015, 15:00–18:00, Poster B

Persistent circular currents around holes in graphite interfaces — •Bogdan Semenenko, Annette Setzer, Winfried Böhlmann, and Pablo Esquinazi — Division of Superconductivity and Magnetism, Institut für Experimentelle Physik II,
Universität Leipzig, D-04103 Leipzig, Germany

To prove the existence of persistent circular currents around artificially made holes in graphite flakes with embedded interfaces we used highly oriented pyrolytic graphite (HOPG) with a large density of interfaces. The presence of interfaces in HOPG is responsible for the metallic-like behavior as well as for the superconductivity found in some graphite materials [1,2]. We performed high precision magnetic measurements using a SQUID at temperatures from 5 K to 300 K and maximum magnetic fields between 0.05 T and 5 T applied normal to the holes area. The holes of ∼ 2   µm diameter were produced using a focused Ga⁺ beam microscope. The rest of the graphite surface was protected by a thick layer of PMMA. The measurements show that if we drill holes in the HOPG it is possible to see a relatively large magnetic moment, which remains persistent after removing the applied field. We speculate that this signal originates from circular currents around the holes that flow at the different interfaces (about 100 within the thickness of the graphite flake used).

[1] P. Esquinazi, T. T. Heikkilä, Y. V. Lysogoskiy, D. A. Tayurskii, and G. E. Volovik, JETP Letters 100, 336 (2014).

[2] A. Ballestar et al., New Journal of Physics 15, 023024 (2013).