Superconductors contain tiny tornadoes of supercurrent, called vortex filaments, that create resistance when they move. This affects the way superconductors carry a current.
But a magnet-controlled “switch” in superconductor configuration provides unprecedented flexibility in managing the location of vortex filaments, altering the properties of the superconductor.
The collaborators’ solution overlays the superconductor with a two-dimensional ferromagnetic layer where tiny magnets point in a wide variety of directions. Rearranging those orientations results in a real-time rearrangement of the pinning on the superconducting site. This makes possible multiple, reversible spin cycle configurations for the vortices. Spin is a particle’s natural, angular momentum.
Yong-Lei Wang, research assistant professor in the Department of Physics and first author on the paper, and who is also affiliated with Argonne National Laboratory, had previously described an artificial spin structure, or magnetic charge ice, which could be tuned to various relatively stable configurations. The structures are called ice because they involve patterned atomic deformations similar to that of oxygen bonds when water freezes. In the current study, Jankó proposed applying the system to superconductors.
“We demonstrated that unconventional artificial-spin-ice geometries can mimic the charge distribution of an artificial square spin ice system, allowing unprecedented control over the charge locations via local and external magnetic field,” Wang said. “We show now that such a control over magnetic charges can be exploited in the control of quantum fluxes in a spin-ice/superconductor heterostructure.” He added that the success resulted from close collaboration between experimentalists and theorists.
The research is expected to provide a new setting at the nanoscale for the design and manipulation of geometric order and frustration—an important phenomenon in magnetism related to the arrangement of spins—in a wide range of material systems, Wang noted. These include magnetic skyrmions, two-dimensional materials, topological insulators/semimetals, and colloids in soft materials.
In addition to Jankó, Wang, and Ma, other authors on the paper include Jing Xu, Zhi-Li Xiao, Alexy Snezhko, Ralu Divan, Leonidas E. Ocala, John E. Pearson, and Wai-Kwong Kwok of Argonne National Laboratory.
This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357. Z.-L.X. and J.X. acknowledge NSF grant DMR-1407175.
Deanna Csomo McCool and Tammi Freehling contributed to this article.
Originally published by Gene Stowe at science.nd.edu on June 11, 2018.