M. Foltyn, K. Norowski, A. Savin, M. Zgirski, Science Advances 10, eado4032 (2024)
We introduce the Single Vortex Box (SVB) – a nanodevice that allows to treat a single superconducting vortex as a macroscopic, albeit quantized “particle”, which can be created and annihilated on demand with pulses of electrical current. Using the method of fast nanosecond-resolving switching thermometry, we measure the temperature rise and the subsequent thermal relaxation resulting from the expulsion of just a single vortex out of the SVB. Our experiment provides a calorimetric estimation of the dissipation in a superconductor due to a single moving vortex. This is a feat of the fundamental importance that has never been accomplished before for the lack of appropriate tools. Our experiments are pivotal steps towards the development of the vortex electronics i.e. memory cells (where the carrier of information would be a single vortex instead of an electron), superconducting diodes, logical elements, and heat valves.
We can trap a single vortex on demand and remove it from the box with a pulse of electrical current (Fig. 1A). The vortex in the squared-shaped trap can be conveniently detected with the adjacent aluminum nanobridge by probing its critical current. Importantly, the device allows not only to sense different vortex configurations, but also to manipulate them with the aim of the additional pulse, called the Lorentz pulse, which is high enough to expel the vortex, but too low to switch the bridge (Fig. 1A-B). The following testing pulse probes the critical current of the bridge which depends on the vortex state of the box. The change in the vortex configuration can be viewed as analogous to the change in the electron number in a single electron box.
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Fig. 1. A: The layout of the studied nanostructure consisting of an Single Vortex Box (SVB), a Dayem nanobridge, and narrow connecting leads. The Lorentz force FL is exerted on the vortex by the applied Lorentz current pulse IL in the presence of perpendicular magnetic field B. B: The as-received experimental vortex stability diagram: Switching current Isw variation at different magnetic fields controlled by the magnitude of the Lorentz pulse. The sharp transitions in the Isw across IL = Iexp line (the dashed line) are signatures of vortex expulsion at the threshold values of the Lorentz pulse. The high value of Isw indicates no vortex in the box (logical state “0”) and the low value evidences one vortex in the box (logical state “1”). The application of the Lorentz pulse allows to switch between vortex states in a fully controllable and reproducible way. It is a feature required for a memory cell. C: The thermal fingerprint of the vortex leaving SVB obtained for the working point depicted with the white circle on the vortex stability diagram. The broken line represents the exponential fit to the experimental relaxation profile. The abrupt increase in electron temperature (dT ~ 250 mK) following the expulsion of the vortex allows to determine the energy dissipated in the process (dQ = 2 eV) D: Probing protocol involving the reset of the box (I0), manipulation of the vortex with the Lorentz pulse (IL) and the read-out of the critical current of the nanobridge (Itest). |
The patent application describes a method of reading and writing logical information in a superconducting memory cell by applying current pulses to a single vortex captured in a SVB. A Dayem bridge, integrated with the SVB, serves as a vortex detector. The proposed method allows for the permanent storage of logical information by controlling the presence of a single vortex in the SVB using a specific current pulse amplitude. Each logical operation (read/write/reset) is performed by sending just a single short current pulse with amplitudes determined in the SVB calibration. A principle of Read/Write operations is presented in Fig. 2 and Fig. 3.
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