Coherent emission from a stack of long Josephson junctions based on low-temperature superconductors

Abstract

The theory of coherent emission of intrinsic Josephson junctions was applied for calculations of IV-characteristics and ac power of emission of a stack of two inductively coupled long junctions with high density of critical currents (106 A/m2) which were based on low-temperature superconductors (MoRe films). Barriers were made of the mixture of Si and W. Barriers had thickness of about 15 nm. Randomly distributed clusters of tungsten in the thick silicon barrier provided weak links between superconducting MoRe films. The critical temperature of the MoRe superconducting films was 9 K. Calculations were made for the system at the temperature 7.7 K. Random spread of critical currents along the junction leaded to the formation of the zero-field step in the IV-curve. The same zero-field step appeared when edges of the homogeneous junction were loaded by the resistance, the capacitance and the inductance. In the stack of two junctions, strong coherent emission appeared at the zero-field step which corresponded to the in-phase mode of oscillations of voltages.