Czech and Cambridge scientists discover memory effect in a superconductor

Scientists from Charles University and the University of Cambridge have discovered an unusual memory effect in a superconducting material: it can retain information for several hours about how an electrical current previously passed through it.

The finding involves an ultraclean crystal of uranium ditelluride, known as UTe₂. Researchers say it points to a new way superconductors could potentially be used, although practical applications remain uncertain.

The study was published in Nature, Charles University’s Faculty of Mathematics and Physics announced Nov. 6.

Superconductors are materials that, under particular conditions, can carry electrical current without electrical resistance. UTe₂ belongs to a class known as unconventional superconductors.

In the experiment, the crystal retained a state determined by how researchers had applied current to it. Both the strength of the current and the speed at which it changed mattered.

“In principle, it is a memory effect that is uncommon in superconductors,” said study co-author Michal Vališka of Charles University’s Faculty of Mathematics and Physics.

Researchers link the behavior to magnetic vortices inside the material. These are tiny threads of magnetic field surrounded by circulating electrical currents.

Depending on how quickly the applied current changes, the vortices can arrange themselves into an ordered structure or become trapped in a different configuration. That retained arrangement allows the material to preserve information about its previous treatment.

The finding therefore concerns a physical state that persists after changes in current, rather than a finished memory device ready for use in electronics.

The quality of the crystal was essential to observing the effect. Impurities can disrupt or suppress the distinctive properties of unconventional superconductors, Vališka said.

“Preparing ultraclean crystals is an important preliminary step for all subsequent experiments,” he added.

Researchers observed the memory effect at approximately two kelvins, equivalent to about minus 271 degrees Celsius—very close to absolute zero.

Those extreme conditions are a major consideration when assessing what the discovery might eventually make possible. The researchers said it was too early to estimate direct practical uses for the material.

For now, the result offers a new insight into how superconductors behave and how their internal magnetic structures can retain information. Establishing whether that behavior can be put to work outside a laboratory will require further research.