Fiske Steps of Josephson Tunnel Junctions Formed with Normal-Distribution Function

Abstract

Magnetic field dependence of Fiske steps has been investigated using Nb/Al–AlOx/Nb tunnel junctions formed with a normal-distribution function with a dispersion parameter of σ= 0.45. Fiske steps are due to the different resonance mode appearing in the current–voltage characteristics when an external magnetic field is applied to the junctions at 4.2 K. Both positions in the voltage scale and current amplitude of Fiske steps were systematically measured. We found that the amplitudes of the Fiske steps increased gradually, and then decreased monotonically with an increase in magnetic field. All Fiske steps almost completely disappeared at a magnetic field of less than 1 mT, at which the dc Josephson critical current also decreased to less than 10-3 of the maximum. The position of Fiske steps in the voltage scale was analyzed using a diamond-shaped junction which corresponds to a 45-degree-rotated square junction.