Manipulation of Hole-pinned Vortices: Classical and Quantum

Project: Research project

Description

The research outlined in this proposal aims to explore various quasi-static and dynamic (r.f/microwave) properties of thin film (Pearl) vortices pinned on patterned holes in a superconducting film, principally niobium, that is thin on the scale of a London penetration depth. Depending on the phenomenon being examined the holes themselves will be either: i) relatively isolated, ii) closely-coupled pairs (doublets), or iii) repeated to generate one- and two-dimensional closely-coupled arrays. An external magnetic field perpendicular to the film will control the average flux density within the film with special emphasis on those strengths that correspond to an integer (or small fractional) occupation of the holes.
One class of experiments involves a broad band search for resonant responses of vortices pinned on isolated holes, since displacement of the vortex center relative to the hole center generates a restoring force. To our knowledge the characteristic frequency of such a mode has not been carefully examined, in part because such modes are over-damped when the normal core resides within a continuous metal, as opposed to an empty hole which eliminates dissipation associated with core motion.
In more risky experiments we propose to use applied d.c. (or pulsed) currents, either alone or in combination with oscillatory fields, to move vortices between neighboring pairs of holes, down a one-dimensional line of holes, or across an two dimensional array of holes. Motion of vortices on the associated washboard potentials should result in r.f./microwave emissions, the frequency of which is controlled by the hole spacing and the applied current that is in turn controlled by the applied current. Application of an oscillatory current at the hopping frequency should produce Shapiro-like steps in the d.c transport characteristics.
Most speculative is the nature of the quantized vortex states associated pairs of adjacent closely coupled holes. In the presence of quantum-tunneling between the neighboring potential wells, a single vortex pinned on the pair could distribute itself between the wells in a symmetric or antisymmetric manner from which two-state superpositions might be formed, which could be searched for spectroscopically.
The research proposed is necessarily highly speculative in character and only minimally driven by existing theoretical proposals. At the same time, there are many potentially exciting outcomes that offer a strong probability that not only interesting physics, but possible new device concepts, will emerge.
StatusActive
Effective start/end date12/15/1911/30/22

Funding

  • National Science Foundation (DMR-1905742)

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manipulators
vortices
proposals
frequency hopping
microwave emission
superconducting films
niobium
occupation
integers
penetration
dissipation
flux density
spacing
broadband
microwaves
physics
thin films
magnetic fields