Description:

Dr. Wai Kwok: Argonne National Laboratory

Title: Controlling Vortex Matter via Novel Patterned Structures

Abstract: The advent of nanofabrication has opened new venues for controlling vortex matter, which is responsible for the electro-magnetic response of all applied superconductors. In particular, nanohole structures with a variety of intriguing patterns have emerged as a versatile platform for controlling and optimizing vortex pinning in superconductors for enhanced critical current. Magnetic field pinning of vortices with meso and nanoscale magnetic structures has also shown great potential for in-situ manipulation of vortex behavior. Here, I will briefly review the vortex response to a variety of nanostructured hole-arrays in superconductors and in particular, demonstrate that a random pattern, an often-overlooked vortex pinning system, can lead to a significant critical current enhancement over a wide magnetic field range. I will also demonstrate the use of ferromagnetic strips on a superconductor to mimic a vortex triode device and lastly, introduce a novel nano-magnetic patterned structure based on artificial spin-ice rules to realize a globally reconfigurable and locally writable magnetic structure that can subsequently be used to control single flux quanta in a superconducting film. The novel ferromagnetic/superconducting hetero-structure enables switchable and reversible rectification effect of the critical current and
furthermore, enables the experimental study of geometric frustration in a flux quanta system. This work was supported by the Department of Energy, Office of Basic Energy Sciences which also funds Argonne’s Center for Nanoscale Materials (CNM) where the nano-and magnetic patterning and morphological analysis were performed.

Host: John Ketterson