Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 32: Postersession Superconductivity: Josephson Junctions, SQUIDs, Heterostructures, Andreev Scattering, Vortex Physics, Cryodetectors, Measuring Devices, Cryotechnique

TT 32.6: Poster

Mittwoch, 25. März 2009, 14:00–18:00, P1A

Effect of magnetic field on the escape rate in small Josephson junctions — •Kirill Fedorov¹, Alexey Feofanov¹, Ralf Dolata², Brigitte Mackrodt², and Alexey Ustinov¹ — ¹Physikalisches Institut, Universität Karlsruhe (TH), 76131 Karlsruhe, Germany — ²Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany

The escape of a point-like Josephson junction (JJ) from the superconducting state is reduced to the escape of a particle from a metastable state in the washboard potential. In the case of a finite size JJ, this problem becomes considerably more complex since the phase acquires a spatial dependence. We experimentally study the macroscopic quantum tunneling (MQT) and the thermal escape in a JJ, placed in an externally applied magnetic field and compare results with the recent theoretical paper by Yu. N. Ovchinnikov et al. [1]. It has been theoretically predicted that the magnetic field strongly changes the crossover temperature between MQT and thermal escape. The experiments were performed using 5 x 3 µm² niobium JJs with critical current density 1 kA/cm². We have found peculiarities in the escape statistics near the minima of Fraunhofer pattern of the switching current dependence on a magnetic field. A comparison of our experimental results with the Ovchinnikov et al. theory will be presented.

[1] Y. N. Ovchinnikov, A. Barone, and A. A. Varlamov, Phys. Rev. Lett. 99, 037004 (2007).