Tiny quantum electronic vortexes can circulate in superconductors in ways not seen before
Peer-Reviewed PublicationIMAGE: A NEW STUDY BY KTH ROYAL INSTITUTE OF TECHNOLOGY AND STANFORD UNIVERSITY REVISES OF OUR UNDERSTANDING OF QUANTUM VORTICES IN SUPERCONDUCTORS. PICTURED, AN ARTIST’S DEPICTION OF QUANTUM VORTICES. (ILLUSTRATION: GREG STEWART, SLAC NATIONAL ACCELERATOR LABORATORY) view more
CREDIT: GREG STEWART, SLAC NATIONAL ACCELERATOR LABORATORY
Within superconductors little tornadoes of electrons, known as quantum vortices, can occur which have important implications in superconducting applications such as quantum sensors. Now a new kind of superconducting vortex has been found, an international team of researchers reports.
Egor Babaev, professor at KTH Royal Institute of Technology in Stockholm, says the study revises the prevailing understanding of how electronic flow can occur in superconductors, based on work about quantum vortices that was recognized in the 2003 Nobel Prize award. The researchers at KTH, together with researchers from Stanford University, TD Lee Institute in Shanghai and AIST in Tsukuba, discovered that the magnetic flux produced by vortices in a superconductor can be divided up into a wider range of values than thought.
That represents a new insight into the fundamentals of superconductivity, and also potentially can be applied in superconducting electronics.
A vortex of magnetic flux happens when an external magnetic field is applied to a superconductor. The magnetic field penetrates the superconductor in the form of quantized magnetic flux tubes which form vortices. Babaev says that originally research held that quantum vortices pass through superconductors each carrying one quantum of magnetic flux. But arbitrary fractions of quantum flux were not a possibility entertained in earlier theories of superconductivity.
Using the Superconducting Quantum Interference Device (SQUID) at Stanford University Babaev’s co-authors, research scientist Yusuke Iguchi and Professor Kathryn A. Moler, showed at a microscopic level that quantum vortices can exist in a single electronic band. The team was able to create and move around these fractional quantum vortices, Moler says.
“Professor Babaev has been telling me for years that we could see something like this, but I didn’t believe it until Dr. Iguchi actually saw it and conducted a number of detailed checks,” she says.
The Stanford researchers found the initial observation of this phenomenon “so incredibly uncommon,” says Iguchi, that they repeated the experiment 75 times in at various locations and temperatures.
The work confirms a prediction Babaev published 20 years ago, which held that in certain kinds of crystals, one part of an electron population of a superconducting material can form a clockwise circulating vortex, while other electrons can form a counter-clockwise vortex simultaneously. “These combined quantum tornadoes can carry an arbitrary fraction of flux quantum,” he says.
“That revises of our understanding of quantum vortices in superconductors,” he says.
Moler affirmed that conclusion. “I have been looking at vortices in novel superconductors for over 25 years, and I have never seen this before,” she says.
Babaev says that the robustness of quantum vortices and the possibility to control them suggests that quantum vortices could potentially be used as information carriers in superconducting computers.
“The knowledge that we gain, the spectacular methods that were introduced by our colleagues Dr. Iguchi and Professor Moler at Stanford, may in a long run be potentially helpful for certain platforms for quantum computation,” Babaev says.
JOURNAL
Science
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Superconducting vortices carrying a temperature-dependent fraction of the flux quantum
ARTICLE PUBLICATION DATE
1-Jun-2023
Finally solved! The great mystery of quantized vortex motion
Explaining the interaction between quantized vortices and normal fluids
Peer-Reviewed PublicationIMAGE: VISUALIZATION OF QUANTIZED VORTEX RING ABOVE THE PLANE (GREEN CURVE), NORMAL-FLUID VORTEX RINGS (REDDISH HALF CIRCLES) view more
CREDIT: MAKOTO TSUBOTA, OMU
Liquid helium-4, which is in a superfluid state at cryogenic temperatures close to absolute zero (-273°C), has a special vortex called a quantized vortex that originates from quantum mechanical effects. When the temperature is relatively high, the normal fluid exists simultaneously in the superfluid helium, and when the quantized vortex is in motion, mutual friction occurs between it and the normal-fluid. However, it is difficult to explain precisely how a quantized vortex interacts with a normal-fluid in motion. Although several theoretical models have been proposed, it has not been clear which model is correct.
A research group led by Professor Makoto Tsubota and Specially Appointed Assistant Professor Satoshi Yui, from the Graduate School of Science and the Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University respectively in cooperation with their colleagues from Florida State University and Keio University, investigated numerically the interaction between a quantized vortex and a normal-fluid. Based on the experimental results, researchers decided on the most consistent of several theoretical models. They found that a model that accounts for changes in the normal-fluid and incorporates more theoretically accurate mutual friction is the most compatible with the experimental results.
“The subject of this study, the interaction between a quantized vortex and a normal-fluid, has been a great mystery since I began my research in this field 40 years ago,” stated Professor Tsubota. “Computational advances have made it possible to handle this problem, and the brilliant visualization experiment by our collaborators at Florida State University has led to a breakthrough. As is often the case in science, subsequent developments in technology have made it possible to elucidate, and this study is a good example of this.”
Their findings were published in Nature Communications.
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About OMU
Osaka Metropolitan University is the third largest public university in Japan, formed by a merger between Osaka City University and Osaka Prefecture University in 2022. OMU upholds "Convergence of Knowledge" through 11 undergraduate schools, a college, and 15 graduate schools. For more research news visit https://www.omu.ac.jp/en/ or follow us on Twitter: @OsakaMetUniv_en, or Facebook.
JOURNAL
Nature Communications
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Imaging quantized vortex rings in superfluid helium to evaluate quantum dissipation
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