AC Quantum Interference Effects in Nanopatterned Nb Microstrips
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The mixed-state dc voltage response of nanopatterned Nb microstrips is investigated by combined microwave (0.5 MHz—1 GHz) and dc electrical resistance measurements. The nanopatterns are arrays of symmetric grooves on the film surface fabricated by focused ion beam milling. They provide a pinning potential of the washboard type for the vortex motion. When subject to a microwave stimulus, the dc current–dc voltage curves of the microstrips exhibit Shapiro steps. The steps occur at voltages V=nV0=nNfΦ0, where n is an integer, N is the number of vortex rows between the voltage leads, f is the microwave frequency, and Φ0 is the magnetic flux quantum. These steps arise as an interference effect when one or a multiple of the hopping period of the coherently moving Abrikosov vortices coincides with the period of the ac drive. When tuning the field value away from the matching field, the steps disappear due to lacking coherence in the motion of the Abrikosov vortex lattice. Dependencies of the dc critical (depinning) current on the microwave power and frequency are reported.
KeywordsAC quantum interference effects Nonlinear vortex dynamics Washboard pinning potential Combined microwave and dc electrical resistance measurements
The author thanks M. Huth for granting access to all the instrumentation involved and R. Sachser for support with nanopatterning and in automating the data acquisition. Discussions with V. A. Shklovskij are gratefully acknowledged. Financial support through the SFB TR 49 project of the German Research Foundation (DFG), the Goethe University funding program “Nachwuchswissenschaftler im Fokus,” and the Vereinigung von Freunden und Fördern of the Goethe University is acknowledged. This work has been done in the framework of the NanoSC-COST Action MP1201.
- 15.Dobrovolskiy, O. V., Franke, J., Huth, M.: submitted (2014)Google Scholar
- 16.Tinkham, M.: Intoduction to Superconductivity (Mineola, New York, 2004)Google Scholar
- 18.Larkin, A. I., Ovchinnikov, Y. N., Exp, J.: Theor. Phys. 41, 960 (1975) [ http://www.jetp.ac.ru/ cgi-bin/index/e/41/5/p960?a=list]ADSGoogle Scholar