Abstract
We present measurements of microwave-induced Shapiro steps in a superconducting nanobridge weak link in the dissipative branch of a hysteretic current-voltage characteristic. We demonstrate that Shapiro steps can be used to infer a reduced critical current and associated effective local temperature. Our observation of Shapiro steps in the dissipative branch hows that a finite Josephson coupling exists in the dissipative state and thus can be used to put an upper limit on the effective temperature and on the size of the region that can be heated above the critical temperature. This work provides evidence that Josephson behaviour can still exist in thermally-hysteretic weak link devices and will allow extension of the temperature ranges that nanobridge based single flux quantum circuits, nanoSQUIDs and Josephson voltage standards can be used.
Highlights
A superconducting weak link (WL) can be realized by creating a narrow constriction between two bulk superconducting electrodes
We demonstrate Josephson behavior in hysteretic nanobridge WL junctions by observation of Shapiro steps and combine the experimental data with our model to estimate the local temperature of the WL
We present experimental evidence of a finite Josephson supercurrent existing in the dissipative state of WL Josephson junctions, demonstrated by the existence of Shapiro steps on the retrapping branch of the in the current-voltage characteristics (IVCs)
Summary
A superconducting weak link (WL) can be realized by creating a narrow constriction between two bulk superconducting electrodes. If the constriction dimensions are made sufficiently small (comparable to 3.5ξ , where ξ is the Ginzburg-Landau coherence length), the WLs are expected to exhibit characteristic Josephson behavior [1]. Nanobridge constrictions can be used instead of traditional Josephson tunnel junctions based on oxide barriers, or superconductor–normal-metal–superconductor (S-N -S) junctions. Nanobridge-constriction junctions can be fabricated using only a single-step lithography process and no oxide layer is required. The lack of an oxide barrier removes a potential source of decoherence, which is an important consideration when building quantum circuits [2]. Nanobridge WLs can be made out of a large range of superconducting materials (both low- and high-Tc), which facilitates incorporation with other circuit elements and nanosensors
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