Flux-flow oscillators based on high temperature superconductors
The results of current development in IPM RAS of fabrication technologies of Josephson junctions based on high-temperature superconductors are presented. We describe the peculiarities of new magnetron sputtering technique of YBCO thin films on YSZ bicrystal substrates and show current-voltage characteristics of the long Josephson junctions, demonstrating visible flux-flow steps. For the opposite magnetic field directions, the flux-flow steps with significantly different height and slope are observed . It is demonstrated that the most probable reason of this discrepancy is recently predicted asymmetry of spatial bias current distribution due to crystallographic anisotropy of bicrystal substrates . We have also studied the Shapiro steps of the fabricated structures. The fractional Shapiro steps with various numbers of visible substeps depending on junction lengths are observed both experimentally and theoretically. Besides, we describe the development of original wet etching technology for fabrication of BSCCO standalone mesas . The produced mesas can be made much thicker than ones usually being studied (roughly from 1 to 20 um). The time required for the fabrication is much smaller in comparison with the standard method of ion milling. The process used is controllable which provides acceptable precision of mesa fabrication. The IV characteristics of the sample showing Josephson nature were obtained.
The work is supported by Russian Science Foundation grant N 16-19-10478.
 L.S. Revin, A.V. Chiginev, A.L. Pankratov, D.V. Masterov, A.E. Parafin, G.A. Luchinin, E.A. Matrozova, and L.S. Kuzmin, Journ. Appl. Phys., 114, 243903 (2013).
 M.Yu. Kupriyanov, M.M. Khapaev, Y.Y. Divin, and V.N. Gubankov, JETP Lett. 95, 289 (2012).
 E.A. Vopilkin, A.V. Chiginev, L.S. Revin, A.N. Tropanova, I.Yu. Shuleshova, A.I. Okhapkin, A.D. Shovkun, A.B. Kulakov and A.L. Pankratov Supercond. Sci. Technol. 28, 045006 (2015).