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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2022

Tunable Magnetic Labyrinth for Abrikosov Vortices

We study Abrikosov vortex dynamics in a superconducting layer covered with an array of T- and I-shaped magnetically soft permalloy elements. Application of the in-plane field H // polarizes thin permalloy bars forming the array and creates a periodic network of mutually perpendicular lines of the attractive or repulsive magnetic potential for vortices along the bar edges, which can be easily tuned by the rotation of H // . Magneto-optical imaging of the vortex trajectories confirms that such a reconfigurable magnetic potential dominates the vortex motion in a wide temperature range and can be a useful tool for manipulating vortices in fluxonic devices for low-loss microelectronics.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Magnetic circuit for Abrikosov vortices: Vortex motion in a periodic labyrinth of magnetic T and I-shaped elements under a superconducting film

Here we explore tailored labyrinth-like vortex motion in a niobium film placed on top of periodic arrays of T and I -shaped permalloy elements by imaging the vortex distribution in magnetic fields applied perpendicular to the superconducting layer under different in-plane polarizations of the TI structure. At low temperatures, we observe pronounced meandering of vortex motion around the TI elements. Remarkably, vortices can easily penetrate the sample along the TI columns even though the average vortex pinning in the patterned area is larger than in a bare niobium film. Accordingly, at temperatures close to the superconducting transition temperature, T c , the voltagecurrent curves in the patterned area show an earlier departure from the zero-resistivity state at small currents, followed by slower growth with increasing current as compared to the un-patterned film. We present a model based on magnetostatic interactions between magnetic charges at the edges of the polarized TI-elements and single magnetic charges of induced vortices to account for this behavior. We expect that similar magnetic structures imposing labyrinth-like vortex motion could be used for collective entanglement of vortices envisioned in quantum circuit operations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Dissipative and fast-timescale phenomena in superconductors

This project explored new effects and regimes that unfold in superconductors as they are pushed to ex treme and unprecedented conditions of electric field, power densities, vortex velocities, etc. Besides their own novelty, these phenomena yield fundamental in formation about the superconducting state and its parameters, as well as its practical limits for techno logical applications. Furthermore some of these ef fects (such as formation of phase slip processes and the acceleration of superfluid) are time dependent on time scales such as quasiparticle-phonon energy re laxation and gap relaxation. This project used fast low-duty-cycle pulsed signals to first of all access these regimes without excessive heating and secondly to observe directly in the time domain the temporal unfolding of these phenomena on nanosecond time scales. This project led to the discovery of new effects in the transport behavior in superconductors, provided new information on fundamental parameters, and helped establish intrinsic strengths and limitations of different superconducting materials for ap plications. The primary tools developed for extending the range of measurable dissipation densities and observation of short time-scale phenomena were fast pulsed-current and pulsed-voltage sources, and fast high-CM-rejection detection circuitry. This allowed conducting measurements at power densities in the 10 10 W/cm 3 range, and at E ~ 1 kV/cm and v Φ ~10 km/s. Also developed was the ability to simultaneously track current I(t) and voltage V (t) and cross correlate them with sub-nanosecond temporal resolution. A recent angle of this project was the exploration of subtle phenomena at low current densities, especially for the magnetic field orientation parallel to the plane of the films. Through modifications of the pulsed tube closed cycle cryostat, we developed methods for attaining low-noise and high temperature-stability conditions. This led to the observation of novel dimensional effects related to the mixed state and vortex matter, and to a new type of magnetoresistance oscillation.

36 MATERIALS SCIENCE↗