Dr. Eley will talk on, "Resistance is Not Futile: Pinning Down Elusive Vortices in Superconductors."
Though superconductors are revered for their ability to carry dissipation-free supercurrents below a material-dependent critical current (Jc), the seemingly inconspicuous action of vortices can introduce dissipation even for currents well below Jc. In type II superconductors (including high-Tc cuprates, iron-based superconductors, and MgB2) immersed in high enough magnetic fields, vortices are formed by the penetration of magnetic flux and can be moved by current-induced forces and thermal energy. Vortex
motion can be disruptive: it limits the current-carrying capacity in wires, can cause losses in microwave circuits, and, more generally, can induce phase transitions. Understanding vortex dynamics is a formidable challenge because of the complex interplay between
moving vortices, material disorder (defining pinning sites) that can counteract vortex motion, and thermal energy that can cause vortices to escape from these pinning sites. In particular, we cannot precisely predict the rate of thermally activated vortex motion
(creep) in a given sample, and tuning the creep rate by modifying the microstructure is typically achieved by means of trial and error. Furthermore, common techniques to enhance Jc by adjusting the disorder landscape (e.g., irradiation or incorporation of nonsuperconducting inclusions) are often accompanied by unfavorable increases in the creep rate.
In this talk, I will discuss the importance of minimizing creep and my efforts to better understand vortex creep. I will cover results from studies of a wide variety of materials. Additionally, I will present our proposal of the existence of a universal minimum realizable creep rate that depends on material parameters. This limitation is of both fundamental and technological significance: it provides new clues about the interplay between material parameters and vortex dynamics and about how to engineer materials with slow creep. This hard constraint, applicable at low temperatures and fields, has two important implications: first, the creep problem in high-Tc superconductors cannot be fully eliminated and there is a limit to how much it can be ameliorated; and second, we can predict that any yet-to-be-discovered high-Tc superconductors will have fast creep. Lastly, I will end by briefly introducing other on-going research projects in our lab, including
studying quantum vortex creep, the dynamics of skyrmions (vortex-like structures that form in certain magnetic materials), and the origin of decoherence mechanisms in superconducting circuits.
Serena Eley is an experimentalist and Assistant Professor of Physics at the Colorado School of Mines. She earned her B.S. in physics at the California Institute of Technology then worked at
the International Superconductivity Technology Center in Tokyo, Japan as a Henry Luce Scholar before earning her Ph.D. in physics at the University of Illinois. Her dissertation work, for which
she received the John Bardeen Award, explored proximity effects and vortex dynamics in nanostructured superconductors, revealing behavior that deviated strongly from conventional proximity effect theories. After graduate school, she worked at Sandia National Laboratories on Si-based devices designed for use as spin quantum bits and as a postdoctoral researcher at Los Alamos National Laboratory on vortex dynamics in superconductors. Currently, Professor Eley’s research group studies the effects of disorder on the properties of quantum materials and devices. More specifically, they focus on understanding vortex-defect interactions in superconductors, mitigating materials related issues that limit superconducting circuit operation, and skyrmion-defect interactions in magnetic materials.
If you would like to attend this seminar please email Mary Sullivan at email@example.com for the zoom link.
Wednesday, February 24, 2021 at 4:30pm to 5:30pmVirtual Event
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