IJS researchers discover new unusual quantum effect

Under the quantum effect in question, properties of tantalum disulphide, a quantum material, undergo significant modification if the material is placed into a cooled optical cavity.

One of the properties of quantum materials is that their macroscopic properties derive from quantum microscopic phenomena and cannot be understood by classical physics and chemistry alone, the IJS said in a press release.

The materials sometimes behave completely counter-intuitive and tantalum disulphide in particular has been the subject of research for the past 30 years. Its unusual properties, such as its metal-to-insulator transition, have attracted even more attention in the past nine years thanks to research conducted at the institute.

The experiment was set out years ago, when crystals of the right size were grown. The material was synthesised by IJS researcher Petra Šutar. A two-year discussion on experimental results followed, with a deep dive on the topic at last year's International Nonequilibrium Quantum Workshop held in Slovenia.

After preliminary results were analysed and discussed, Dragan Mihailović, head of department for complex matter, and Peter Prelovšek from the department of theoretical physics at IJS, joined forces with foreign researchers in a team led by Daniel Fausti, who works at the University of Trieste and the University of Erlangen-Nürnberg.

The starting point for the experiment was the phenomenon known as vacuum fluctuations, which refers to temporary random changes in the amount of energy at a certain point in space, Mihailović told the STA.

In the experiment, they used mirrors to create a geometrically confined vacuum, which also limited the extent of energy disruptions. When tantalum disulphide was placed between the mirrors, an unusually large change in the insulator-to-metal transition temperature in the crystal was observed.

"The phenomenon is unusual because the material is not in contact with its surroundings during the experiment and the influence of mirrors suggests a strong coupling between the electrons in the material and the quantum fluctuations in the vacuum's electromagnetic field. This results in the transition temperature changing," the institute explained.

Mihailović considers tantalum disulphide exhibiting certain sensitivity during the experiment a remarkable success with potential practical application.

The team's article was published in the high-profile science journal Nature in mid-October. The findings open the way for research into new quantum effects and put tantalum disulphide at the forefront of thought-provoking quantum materials, IJS said.