Figure 1

(Color online) (a) A sketch of a superconducting gear with asymmetric teeth, consisting of six annular IJJs. Superconducting and insulating layers are dark (blue gray) and light (yellow), respectively. Josephson vortices are indicated by circulating supercurrents. The bias current is fed in via the upper electrode and is extracted via the lower electrode (arrows). The lower graph schematically shows the ratchet potential experienced by a fluxon. (b) Optical microscopic image with backside illumination of a chip shows two annular stacks (the gear and a smooth ring) consisting of 30 IJJs. $V_{\pm }$ and $I_{\pm }$ indicate voltage and current contacts to measure the gear. The contacts to the upper part of the gear are hardly visible and, therefore, its edges are shown by the dotted lines.Reuse & Permissions

Figure 2

(Color online) Current-voltage characteristics of (a) the smooth ring measured at $T=4.2\text{K}$ and (b) of the gear measured at $T=8\text{K}$. Upper insets show optical images of the devices. Lower inset in (b) shows a different realization of fluxons trapped in the gear.Reuse & Permissions

Figure 3

(Color online) (a) Optical image of the gear. LTSLM images of IJJ biased (b) on the McCumber state and (c) on the flux flow branch. (d) The geometry used in simulations. The white dot is the “hot spot” of area $1.5\times 1.5\mu {\text{m}}^2$ (with 5% smaller critical current density and resistance), which is moved across the sample during the simulation. Simulated LTSLM images are shown for a bias (e) in the McCumber state and (f) on the flux flow branch.Reuse & Permissions

Figure 4

(a) Measured rectified voltage $V$ across the gear stack as a function of microwave amplitude of a 12 GHz drive at zero dc bias. (b) Simulated $V\left(I_{\text{rf}}\right)$ of a single junction containing one or two fluxons. (c) Simulated $V\left(I_{\text{rf}}\right)$ of a five junction stack containing two fluxons in layer 1 and one fluxon in layer 2. $I_0$ is the intrinsic critical current.Reuse & Permissions