Frequency dependence of giant Shapiro steps in ordered and site-disordered proximity-coupled Josephson-junction arrays

Giant Shapiro Steps in a Superconducting Network of Nanoscale Nb Islands

“…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]. Conversely, when a DC current larger than I c is passed through a Josephson junction, it will start to emit radiation of a fixed wavelength.…”

Giant fractional Shapiro steps in anisotropic Josephson junction arrays

“…Note, that since the RF excitation is experimentally applied by a function generator, the conversion between the applied AC voltage, V rf , and the transmitted AC current, I rf , is a priori unknown (see Supplementary Information Note 2). The pronounced Shapiro response at the voltage values V T n ¼ nðN x À 1ÞΦ 0 ν rf , with N x = 200, indicates that the whole Josephson junction network has a coherent response under RF excitation, in which all N x − 1 = 199 junctions contribute, despite the presence of an unavoidable disorder in the system due to sample fabrication 37 . Figure 2b, shows the experimentally measured frequency dependence for a fixed RF excitation amplitude for Device 1.…”

“…For a current biased system, the width of the Shapiro current plateaus can deviate from the ideal Bessel dependence, expected for a JJ which is voltage biased. For the current biased case the current width of the nth Shapiro step depends in a non-trivial way on the reduced frequency 21,[37][38][39][40] :…”

“…Consequently, the anisotropic JJA is expected to reflect single JJ behaviour, while simultaneously keeping the advantages of high device critical currents and giant Shapiro responses, the array geometry provides. However, disorder in the array, inherent to the fabrication process, might induce broadening of the Shapiro steps 42 . Figure 4c shows the measured and simulated contour map of the differential resistance as a function of the applied magnetic field and reduced DC voltage, V T =V T 1 , for Device 2 at T = 1.8 K. The observed magnetic field dependence can be explained by the variation of the critical current with field at T = 2 K, shown in Fig.…”

Fractional Shapiro steps in resistively shunted Josephson junctions as a fingerprint of a skewed current-phase relationship

“…However, we did not observe a clear oscillatory dependence of the step widths on the drive frequency. This could be explained by smearing of the Shapiro steps due to unavoidable disorder in the Josephson junction array and thermal fluctuations [36].…”