Subharmonic Shapiro steps in Josephson-junction arrays

Giant Shapiro Steps in a Superconducting Network of Nanoscale Nb Islands

“…At B = B 0 , the depression of the dV/dI at the Shapiro step is smaller than without a magnetic field, but at f = 1/2, it is smaller still. Fractional Shapiro steps observed in previous studies [1,2,4] are not clearly visible. The reason for this could be that the coupled power of the RF radiation is too small.…”

“…The dip is clearly not present in the unirradiated case. The depression in dV/dI is smaller than in similar studies of regular square arrays [1,2,4], but a direct comparison is difficult because in this setup, it is unknown how much power the pickup loop actually converts into radiation. Figure 2 shows transport measurements with constant RF radiation for different magnetic fields.…”

“…When a large number of identical junctions is connected in series, they will all resonate at the same current resulting in a voltage plateau at exactly N* V SS . These steps are called giant Shapiro steps [1,9] and can be used as voltage standards [10]. Moreover, they have been observed in cuprates [11] and disordered arrays [12].…”

“…In particular, the zero-temperature phase can be tuned to a conductor [3] and an insulator [5] by making the distance between grains larger than the coherence length. The increased level of control over the spatial complexity and disorder in a regular square array of nanostructured superconductors has made Nicola Poccia nicola.poccia@utwente.nl nicola.poccia@nano.cnr.it 1 MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, Netherlands 2 NEST Istituto Nanoscienze-CNR & Scuola Normale Superiore, Pisa, Italy possible the observation of a vortex Mott insulator-to-metal transition which occurs far from equilibrium [6].…”

“…It is known that regular square arrays of BCS-type superconductors in the shape of crosses [1,2], dots [3], or anti-dots [4,5] on top of both metallic and insulating substrates have been investigated on varied length scales. In particular, the zero-temperature phase can be tuned to a conductor [3] and an insulator [5] by making the distance between grains larger than the coherence length.…”