Full text loading...
(a) Scanning electron micrograph of the l = 20 μm type A SINIS20 turnstile showing the superconducting Al leads connected to the Cu metal island via AlO2 barrier junctions and the gate electrode used to regulate the potential of the island. (b) shows the type B SINISopen geometry sample where the normal metal traps are within 200 nm of the junctions and the leads open up straight from the junction. In (c), the full length l of the superconducting line of sample SINIS20 between the junction and the trap is visible as well as the quasiparticle traps formed by overlapping Cu and Al shadows. A sketch of the basic measurement circuitry is depicted and (d) shows the IV characteristics of the turnstile.
(a) and (b) show the normalized current through the oxide trap turnstile of geometry l = 20 μm smoothed over 5 data points as a function of for gate voltages varying between and . The charge stability measurement plotted in (a) was performed in a sample stage with a single cover; (b) shows measurements of the same sample in an indium sealed two-cover stage. In (c) and (d), we plot the normalized current computed with a simulation based on sequential tunneling for the situations of (a) and (b), respectively. The inset of (d) shows the quasiparticle density inferred from the temperature reproducing the measured current inside the superconductor gap as a function of the length l of the isolated superconducting line.
Current plateaus under pumping. Current through the turnstile as a function of the gate modulation amplitude measured on the type A SINIS20 sample at (a) 1 MHz, (b) 10 MHz, and (c) 20 MHz sinusoidal modulation frequency and on the type B sample SINISopen in (d) at 20 MHz. The pump was operated at bias voltage values of (blue dots), (green dots), and (red dots). Fits from simulations including two-electron Andreev processes are displayed as solid black lines; dashed black lines are simulations only including single electron processes.
Quasiparticle density as a function of the driving gate voltage f. Fits to measurements including first and second order tunnelling processes are displayed as dots and quasiparticle densities derived from the diffusion model are displayed as solid lines. We compare two type A samples with delayed relaxation, SINIS20 (blue) and SINIS5 (green) and one type B sample SINISopen (red). Diagrams of the sample geometries are displayed in the upper part of the figure, dark colours representing quasiparticle traps, lighter areas the isolated superconducting lines, and the small black bulks the normal metal islands. Below, a diagram shows the two pathways to quasiparticle excitation, during pumping via the normal metal island and through interactions with the electromagnetic environment.
Article metrics loading...