Dual flux-to-voltage response of YBa₂Cu₃O_7−δasymmetric parallel arrays of Josephson junctions

Abstract

Fig. 4b and from 0.5 mA to 1mA (-1 mA to -0.5 mA) in Fig. 5a. Also, the amplitude of voltage modulation is considerable larger for negative currents relative to the positive currents. It is important to note that the families of V(I ctrl ) recorded for different current biases I plotted in Figs. 3b, 4b and 5b, they all lack inversion symmetry with respect to 0. This is because the PAJJ is not magnetically screened and therefore the presence of the earth magnetic field breaks such symmetry. Since the perpendicular component to the PAJJ planar structure of the earth magnetic field B normal is about 25 T it requires a significant shifting along the I ctrl current axis in order to compensate for the earth magnetic field and therefore recover the inversion symmetry. Indeed, the magnetic field corresponding to I ctrl =1.8mA (the current period of V(I ctrl ) curves) is about 2.4 T which is much smaller than B normal . The differences in the IVCs and V(I ctrl ) between the positive and the negative current biases are far less pronounced at temperatures below 60K. An example is shown in Fig. 6 for T=57.5 K. Similar characteristics have been measured at several other temperatures below 60K, namely, at 4.7K, 10K, and 30K.Indeed, the IVCs have a good degree of symmetry at these temperatures (see Fig.6a). Also, in this temperature range the V(I ctrl ) response becomes aperiodic (see Fig.6b) due to a significant suppression of the flux-flow modes due to a decrease in the dissipation coefficient 1/R N (or damping) with temperature (here R N is the normal resistance of the Josephson junction). A similar suppression of the flux-flow with decreasing T has been previously observed (both theoretically and experimentally) in PAJJs made of niobium low temperature superconductors [4,5].8 ConclusionIn conclusion, we have shown that an inductive asymmetric loop configuration within the array implemented in our PAJJ leads to a significant difference in the flux-flow for positive current biases relative to negative current biases and consequently to a corresponding different qualitative flux-to-voltage response. To achieve both an enhanced current amplification [11] and an enhanced microwave power generation [12] a PAJJ has to be operated in a regime of enhanced flux-flow, i.e., it should be biased with a positive current.The degree of asymmetry of our design can be further extended to enhance the contrast in the directional flux-flow and to improve PAJJs performances in these applications.

Magnetic field tunable vortex diode made of YBa2Cu3O7−δ Josephson junction asymmetrical arrays

“…Indeed, in ratchets based on asymmetric current bias configurations, the environmental noise (of electrical/ magnetic nature) can interfere destructively with the current bias and decrease its efficiency. Ratchets based on a device's structural/fabrication asymmetry have been recently fabricated and they showed remarkable features such as a record current amplification at temperatures above 77 K, 36 a dual flux-to-voltage response, 37 and an ability to amplify the self-induced electromagnetic radiation. 38 However, due to their complexity (the design consisted of a parallel-array of 22 Â 20 JJs connected by variable areas of SQUID-like holes), such devices have not been simulated numerically, and consequently, the physics behind their behaviour could not be fully understood.…”

Evidence for vortex splitting at the grain boundary in long YBa2Cu3O7−δ grain boundary junctions

“…As θ decreases, V m increases, and the step becomes wider, meanwhile, the height of the step gradually decreases. We relate these steps to the flux-flow (velocity matching) steps, as the height and the scope of the steps obey the same monotonically decreasing relationship [15,[22][23][24][25][26][27][28]. The appearance of flux-flow steps for long GB junctions is due to the continuous Josephson vortex flow in the GB plane [22][23][24][25][26][27][28].…”

“…We relate these steps to the flux-flow (velocity matching) steps, as the height and the scope of the steps obey the same monotonically decreasing relationship [15,[22][23][24][25][26][27][28]. The appearance of flux-flow steps for long GB junctions is due to the continuous Josephson vortex flow in the GB plane [22][23][24][25][26][27][28]. In previous studies, there has been a research into the vortex-flow steps that appeared in the I-V curves of long Josephson junctions such as low-T c superconductor-insulator-superconductor long junctions, low-T c superconductor-normal conductor-superconductor long junctions, and high-T c GB long junctions [22][23][24][25][26][27][28][29][30][31].…”

Vortex ratchets based on asymmetric arrays of Josephson junctions

“…A quantitative comparison between the two would require a more advanced theoretical model which is beyond the scope of this report. The 440 asymmetric JJ array consists of 22 identical sets of 20 JJ each [24][25][26]. All 440 JJ are 3 µm wide, the junctions are separated by superconducting loops of identical width (3 µm) but variable length.…”

“…Superconducting vortex ratchets can also be based on a device's asymmetric fabrication using either JJ arrays [19,20] or asymmetric superconducting quantum interferometer devices (SQUIDs) [21][22][23]. Recently parallel JJs array devices have been fabricated based on structural asymmetry [24][25][26]; such devices have not been simulated numerically due to their complexity. Here we present numerical simulations of three less complex structural asymmetric designs [27], as well as, ratchet-eect measurements taken on several designs implemented experimentally.…”