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TT: Tiefe Temperaturen

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

TT 7.57: Poster

Montag, 27. März 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. Koelle¹ — ¹Physikalisches 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 T_c via an optical, essentially noiseless heating system. Measurements of critical current I_c vs. magnetic flux density B close to T_c reveal pronounced matching effects, i.e. an enhancement of I_c 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).