Nav: Home

Designing a better superconductor with geometric frustration

June 11, 2018

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, according to a new paper in Nature Nanotechnology.

"We work on superconductors and how to make them better for applications," said Boldizsár Jankó professor in the Department of Physics at the University of Notre Dame and co-corresponding author on the paper. "One of the major problems in superconductor technology is that most of them have these filaments, these tiny tornadoes of supercurrent. When these move, then you have resistance."

Researchers have been trying to design new devices and new technologies to "pin," or fasten, these filaments to a specified position. Previous efforts to pin the filaments, such as irradiating or drilling holes in the superconductor, resulted in static, unchangeable arrays, or ordered arrangements of filaments. A new, dynamic system discovered by Jankó and collaborators will enable ongoing adjustments, altering the material's properties over time. The results of the research were published June 11 in Nature Nanotechnology in a paper titled "Switchable geometric frustration in an artificial-spin-ice/superconductor hetero-system."

The collaborators' solution overlays the superconductor with an artificial spin ice consisting of an array of interacting nanoscale bar magnets. Rearranging the magnetic orientations of those nano-bar magnets 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.

"The main discovery here is our ability to reconfigure these spinning sites reversibly and instead of having just one spin cycle configuration for the vortices, we now have many, and we can switch them back and forth," Jankó said. The magnetic charges have the same pinning effect as drilled holes in other systems but are not limited to a static configuration, he described. For example, the magnets could be arranged to create more or less resistance in the superconductor. The elementary unit potentially could be combined into a circuit capable of logic manipulation.

Yong-Lei Wang, research assistant professor in the Department of Physics and co-first/co-corresponding author on the paper, who is also affiliated with Argonne National Laboratory and Nanjing University, 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 fields," 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.

Because the control of the quantum fluxes is difficult to visualize in an experiment, simulations were required to successfully reproduce the results, said Xiaoyu Ma, a doctoral student in the Department of Physics who conducted the computer simulation in the study and is the co-first author on the paper. The simulations allowed researchers to see the detailed processes involved. "The number of vortex configurations that we can realize is huge, and we can design and locally reconfigure them site by site," Ma said. "This has never been realized before."

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.

"This could lead to novel functionalities," Wang said. "We believe this work will open a new direction in application of geometrical frustrated material systems."
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.

University of Notre Dame

Related Physics Articles:

Diamonds coupled using quantum physics
Researchers at TU Wien have succeeded in coupling the specific defects in two such diamonds with one another.
The physics of wealth inequality
A Duke engineering professor has proposed an explanation for why the income disparity in America between the rich and poor continues to grow.
Physics can predict wealth inequality
The 2016 election year highlighted the growing problem of wealth inequality and finding ways to help the people who are falling behind.
Physics: Toward a practical nuclear pendulum
Researchers from Ludwig-Maximilians-Universitaet (LMU) Munich have, for the first time, measured the lifetime of an excited state in the nucleus of an unstable element.
Flowers use physics to attract pollinators
A new review indicates that flowers may be able to manipulate the laws of physics, by playing with light, using mechanical tricks, and harnessing electrostatic forces to attract pollinators.
Physics, photosynthesis and solar cells
A University of California, Riverside assistant professor has combined photosynthesis and physics to make a key discovery that could help make solar cells more efficient.
2-D physics
Physicist Andrea Young receives a 2016 Packard Fellowship to pursue his studies of van der Waals heterostructures.
Cats seem to grasp the laws of physics
Cats understand the principle of cause and effect as well as some elements of physics.
Plasma physics' giant leap
For the first time, scientists are looking at real data -- not computer models, but direct observation -- about what is happening in the fascinating region where the Earth's magnetic field breaks and then joins with the interplanetary magnetic field.
Nuclear physics' interdisciplinary progress
The theoretical view of the structure of the atom nucleus is not carved in stone.

Related Physics Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#514 Arctic Energy (Rebroadcast)
This week we're looking at how alternative energy works in the arctic. We speak to Louie Azzolini and Linda Todd from the Arctic Energy Alliance, a non-profit helping communities reduce their energy usage and transition to more affordable and sustainable forms of energy. And the lessons they're learning along the way can help those of us further south.