THEORY AND EXPERIMENT ON ELECTROMAGNETIC-WAVE-PROPAGATION VELOCITIES IN STACKED SUPERCONDUCTING TUNNEL STRUCTURES

Characteristic velocities of the electromagnetic waves propagating in vertically stacked Josephson transmission are theoretically discussed. An equation for solving n velocities of the waves in an n Josephson-j unction stack is derived. The solutions of two- and threefold stacks a re especially focused on. Furthermore, under the assumption that all p arameters of the layers are equal, analytic solutions for a generic N- fold stack are presented. The velocities of the waves in two- and thre e-junction stacks by Nb-Al-AlOx-Nb systems are experimentally obtained by measuring the cavity resonance (Fiske step) modes. Comparison of t he theory with the experimental data reveals good quantitative agreeme nt.