Superfluidity in Quantum Systems

Cold atoms represent an exciting area of research for condensed matter physicists. Ever since 1995, when scientists created the first ultracold quantum gas, experiments continue to uncover fascinating behaviours of matter at the quantum level.

At ultra-low temperatures scientists can change, at will, the interaction between atoms, a luxury that is unheard of in ordinary solid and liquid systems. This new freedom permits experimental study of issues that had long been abandoned as insoluble and unverifiable.

One quantum behaviour that is of great interest to researchers is the phenomenon of superfluidity, when materials, under extremely cold temperatures and pressure, flow without friction. Researchers in ICTP's Condensed Matter and Statistical Physics section have been looking at what happens when disorder is introduced to a Boson superfluid. In particular, they have analysed and documented the phase transition of a superfluid state to a disorder-induced, insulator state. Their results, which have been published in the 25 October issue of Physical Review Letters (PRL 107, 185301 2011), make an important contribution to the study of superfluidity in quantum systems.

Sebnem Gunes Söyler, first author of the paper and a postdoctoral fellow at ICTP, explained that the main result of the analysis is that this transition phase had an almost unobservable response to the disorder effect. "It was surprising that the weak but finite disorder actually didn't shift the transition point," she said, adding, "Our results are pretty accurate, but will lead to another work, as we want to study different types of disorder in lattice or uniform distributed systems, to see how this point changes, and to see if it is a global effect, because actually this transition point between superfluid to Bose Glass point depends on the type of disorder used."

Co-authors of the article include ICTP scientist Mikhail Kiselev, and N. V. Prokof'ev and B. V. Svistunov of the University of Massachusetts, USA.

ICTP hosted a workshop last summer on superfluids and insulators; for details, see the workshop website.