A thin interlayer is incorporated in ramp-type Josephson junctions to obtain an increased transparency. The interlayer restores the surface damaged by ion milling and has the advantage of an all in situ barrier deposition between two superconductors, leading to clean and well-defined interfaces. The method has been applied to Josephson junctions between high (YBa2Cu3O7–) and low temperature (Nb) superconductors, separated by a Au barrier. Transmission electron microscopy images of these junctions reveal crystalline YBa2Cu3O7– up to the interface with the Au barrier. The junctions have improved critical current density values exceeding 20 kA/cm2, normal state resistances of 3×10–8 cm2 and IcRn products of 0.7 mV at 4.2 K. Furthermore, the junction properties can be controlled by varying the Au barrier thickness.
Smilde, H. J. H., Hilgenkamp, J. W. M., Rijnders, A. J. H. M., Rogalla, H., & Blank, D. H. A. (2002). Enhanced transparency ramp-type Josephson contacts through interlayer deposition. Applied physics letters, 80(24), 4579-4581. https://doi.org/10.1063/1.1485305