Modeling Bloch Oscillations in Nanoscale Josephson Junctions
Heli C. Vora, Richard Kautz, Sae Woo Nam, Jose A. Aumentado
Bloch oscillations in nanoscale Josephson junctions with a Coulomb charging energy comparable to the Josephson coupling energy are explored within the context of a model previously considered by Geigenmüller and Schön that includes Zener tunneling and treats quasiparticle tunneling as an explicit shot-noise process. The dynamics of the junction quasicharge are investigated numerically using both Monte-Carlo and ensemble approaches to calculate voltage--current characteristics in the presence of microwaves. We examine in detail the origin of harmonic and subharmonic Bloch steps at dc biases I=(n/m)ef induced by microwaves of frequency f and consider the optimum parameters for the observation of harmonic (m=1) steps. We also demonstrate that the GS model allows a detailed semi-quantitative fit to experimental voltage--current characteristics previously obtained at the Chalmers Institute of Technology, confirming and strengthening the interpretation of the observed microwave-induced steps in terms of Bloch oscillations.