ICTP-SAIFR colloquium discusses Quantum Spin Liquids

Last Wednesday, the traditional colloquium held at ICTP-SAIFR addressed the topic of “quantum spin liquids”. Rodrigo Pereira, from the University of São Paulo (USP-São Carlos), spoke about this state of matter that arises when Mott insulators are subjected to low temperatures. Under these conditions, unlike band insulators, it’s possible to modify the spin of its electrons, making their magnetic properties more interesting.

Among the key features of “quantum spin liquids” are the facts that there is no magnetic order of spins – the same way there is a certain disorder of particles in the liquid state of matter when compared to solids – and there is rotational symmetry of spins. Although the existence of a material that could behave as a “quantum spin liquid” has not yet been discovered, there are some possible candidates. In case one of them is confirmed, it would be possible to obtain a superconducting material by altering electron density and inducing a phase transition from the “quantum spin liquid” to the superconductor.

“The area of ​​’quantum spin liquids’ is interesting because it presents theoretical challenges, but also have experimental motivations”, says Pereira.

First proposed in 1973 by American physicist Philip Warren Anderson, the “quantum spin liquid” was at the time a purely theoretical state. In the following decades, with the motivation of studying new states of matter and the growing interest in superconductors, scientists began to wonder whether it was possible to study “quantum spin liquids” in more dimensions, and if this material could actually exist.

“The main motivation for studying ‘quantum spin liquids’, from a theoretical point of view, is that such a material would present exotic properties that wouldn’t fit into current classifications of states of matter, what would open possibilities for new theories”, says Pereira. “Quantum spin liquids may also make an interesting connection between the areas of Condensed Matter and High Energy Physics”.

One of the main candidates to prove the existence of the “quantum spin liquid” state is the herbertsmithite. This mineral was discovered in 1972, in Chile. In 2012, a synthesized form showed some characteristics of “quantum spin liquids”, and studies are still underway to confirm the phenomenon.

The experimental reasons to study “quantum spin liquids” are related to the possibility of the material acting as a superconductor in more natural temperatures. As the materials used today as superconductors require an extremely low temperature to not have electrical resistance, a superconducting material that could work in higher temperatures, among other applications, could lead to large savings in energy transportation.