An artist’s depiction of quantum vortices. Image: Greg Stewart, SLAC National Accelerator Laboratory.
An artist’s depiction of quantum vortices. Image: Greg Stewart, SLAC National Accelerator Laboratory.

Within superconductors, little tornadoes of electrons, known as quantum vortices, can occur that have important implications for superconducting applications such as quantum sensors. Now, an international team of researchers has reported, in a paper in Science, the discovery of a new kind of superconducting vortex.

Egor Babaev, professor at KTH Royal Institute of Technology in Stockholm, Sweden, says the study revises the prevailing understanding of how electronic flow can occur in superconductors, which is based on work on quantum vortices that was recognized with the 2003 Nobel Prize. The researchers at KTH, together with colleagues from Stanford University, TD Lee Institute in China and the National Institute of Advanced Industrial Science and Technology (AIST) in Japan, discovered that the magnetic flux produced by vortices in a superconductor can be divided up into a wider range of values than previously thought.

This discovery offers a new insight into the fundamentals of superconductivity and could also potentially find use in superconducting electronics.

A vortex of magnetic flux arises 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. According to Babaev, it was originally thought that when quantum vortices pass through superconductors, they each carry one quantum of magnetic flux, because arbitrary fractions of quantum flux were not considered in earlier theories of superconductivity.

Using the Superconducting Quantum Interference Device (SQUID) at Stanford University, Babaev’s co-authors, Yusuke Iguchi and Kathryn Moler, showed at a microscopic level that quantum vortices with fractions of quantum flux can exist in a single electronic band. The team was able to create these fractional quantum vortices and move them around.

“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,” Moler says.

The Stanford researchers found their initial observation of this phenomenon “so incredibly uncommon”, says Iguchi, that they repeated the experiment 75 times 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 simultaneously form a counter-clockwise vortex.

“These combined quantum tornadoes can carry an arbitrary fraction of flux quantum,” he explains. “That revises our understanding of quantum vortices in superconductors.”

Moler confirmed that conclusion: “I have been looking at vortices in novel superconductors for over 25 years, and I have never seen this before.”

Babaev says that the robustness of quantum vortices and the possibility for controlling them suggests that they 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.”

This story is adapted from material from KTH Royal Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.