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Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

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

TT 7.57: Poster

Monday, March 27, 2006, 14:00–17:45, P1

Commensurability and ratchet effects in Nb thin films with artificial pinning site — •M. Kemmler1, C. Gürlich1, H. Pöhler1, M. Siegel2, M. Neuhaus2, R. Kleiner1, and D. Koelle11Physikalisches Institut - Experimentalphysik II, Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen — 2IMS, Universität Karlsruhe, Hertzstr. 16, D-76187 Karlsruhe

We investigate artificial pinning arrays - formed by (sub-) micron-sized holes (antidots) of various shape in Nb thin films. For measurements of electric transport and low-frequency noise we use a highly sensitive liquid Helium-cooled dc SQUID amplifier. The sample temperature is controlled and stabilized close to the Nb transition temperature Tc via an optical, essentially noiseless heating system. Measurements of critical current Ic vs. magnetic flux density B close to Tc reveal pronounced matching effects, i.e. an enhancement of Ic when the flux line lattice is commensurate with the antidot lattice. We also find such matching effects in the low-frequency flux noise, i.e. a suppression of the flux noise at the matching fields. By reshaping the artificial pinning sites it is possible to construct Abrikosov-vortex-ratchets [1,2]. For our measurements of ratchet effects triangular antidots are used. Measurements of the vortex response to an ac current drive reveal pronounced voltage rectification. We find a strong dependence of the voltage output on temperature, ac current amplitude and the magnetic field.

[1] J. Van de Vondel et al., Phys. Rev. Lett. 94, 057003 (2005) .

[2] J. E. Villegas, et al., Science 302, 1188 (2003).

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