Probing Confined Vortices with a Superconducting Nanobridge

Abstract

We realize a superconducting nanodevice in which vortex traps in the form of an aluminum square are integrated with a Dayem nanobridge. We perform field-cooling of the traps arriving to different vortex configurations, dependent on the applied magnetic field, to demonstrate that the switching current of the bridge is highly sensitive to the presence and location of vortices in the trap. Our measurements exhibit unprecedented precision and ability to detect the first and successive vortex entries into all fabricated traps, from few hundred nm to 2 µm in size. The experimental results are corroborated by Ginzburg-Landau simulations, which reveal the subtle yet crucial changes in the density of the superconducting condensate in the vicinity of the bridge with every additional vortex entry and relocation inside the trap. An ease of integration and simplicity make our design a convenient platform for studying dynamics of vortices in strongly confining geometries, involving a promise to manipulate vortex states electronically with simultaneous in situ control and monitoring.

Quantum thermodynamics with a single superconducting vortex

“…For superconducting strips of width W, this minimum is separated with the Bean-Livingston barriers from the edges of the strip and is first established when magnetic field exceeds the threshold value, i.e., B 0 ∼ πΦ 0 4W 2 (28)(29)(30). This prediction holds for superconducting strips (31) but qualitatively (up to a numerical factor of the order of unity) is also correct for the squared zero-dimensional (0D) confinements that are studied below (32). The presented model also predicts that the trapped vortex can be expelled from the nanostructure by application of the pulse of electrical current, which tilts the potential energy and removes the local energy minimum: Because of the Lorentz force, the vortex is pushed to the side of the square, and, eventually, it escapes out of the sample (Fig.…”

“…1E), which guarantees type II superconducting behavior of our device (text S2). The SVB is attached to a short Dayem nanobridge, whose critical current is sensitive to the vortex state of the box ( 32 ). The structure (box + nanobridge) is connected to the contact pads through 15-μm-long and 300-nm-wide leads.…”

“…The switching current of the bridge is sensitive to the local population of QPs, which, in turn, depends both on temperature and distribution of the Meissner screening currents. The first property makes the bridge a sensitive thermometer ( 17 ), and the second one allows for the detection of magnetic field and vortices, even if they are not expelled ( 32 ). The standard probing protocol is extended by the application of two additional pulses in each cycle, which precede the actual testing pulse (Figs.…”