Nanoscale physics

Microware properties of MoxRe1-x Josephson junctions
Rudenko E.M.1, Korotash I.V.1, Krakovny A.O.1, Perepelitsa V.K.1, Malyshev V.Yu.2, Prokopenko O.V.2
1 G.V. Kurdyumov Institute for Metal Physics, N.A.S. of Ukraine, Boulevard of Academician Vernadsky, 36, Kyiv-03142, Ukraine. 
E-mail: metall@imp.kiev.ua 
2 Taras Shevchenko National University of Kyiv, Volodymyrska street, 64/13, Kyiv-01601, Ukraine

Josephson junctions (JJs) are widely used in practice to create nanoscale devices having unique properties (extremely high sensitivity to weak dc or ac magnetic fields, very low noise, the possibility of operation in a wide frequency range, etc.). The efficiency of these devices is mainly limited by the properties of utilized superconductor. Among existing low-temperature superconductors MoxRe1-x alloy is now considered as promised for a number of applications, but its microwave properties have not been sufficiently studied yet. In this work we experimentally study microwave properties of MoxRe1-x JJs and analyze an efficiency of microwave/dc energy conversion in such structures.
Fabricated JJs Mo0.55Re0.45(200 nm)-Al2O3(1 nm)-Pb/Sn(150/30 nm) were deposited on sapphire substrate (8×20×0.5 mm) by using magnetron sputtering and thermal deposition techniques. In experiment, MoxRe1-x JJs were located inside the measuring section based on a standard 3-cm rectangular waveguide. Input microwave signal, generated by the source G4-109, was adjusted and controlled by an attenuator having attenuation error less than 2%; the power of the signal applied to the sample via a coaxial-pin antenna was varied from 10–3 to 10–14 W.
Current-voltage characteristic of JJs, measured by a four-probe method at the temperature of 4.2 K, indicated that the behavior of studied JJs was similar to the behavior of a tunnel junction. The dependence of the critical Josephson current on bias dc magnetic field was rather different from that of typical "Fraunhofer" curves; nevertheless a significant suppression of the critical current in the magnetic field was observed. Under the action of external microwave signal having the frequency of 8.6 GHz the critical Josephson current was suppressed completely, when the signal attenuation was off. As the signal was attenuated by 15 dB (signal power was about 3 10–5 W) the voltage steps of approximately 20 μV width were observed on the junction’s current-voltage characteristic indicating that the superconducting structure Mo0.55Re0.45-Al2O3-Pb/Sn is suitable for the detection of weak microwave signals.