(Featured image: Artist's rendering of the Mitrovic lab at Brown University, depicting chaos at high temperatures and order at low temperatures. Courtesy of Jelena Berenc.)
At ordinary temperatures, chaos is the rule. All particles undergo random motion, the speed of which increases with temperature. The same is true of the electrons that surround the nucleus of every atom, determining its behavior and how it will interact with other atoms.
We have learned from quantum mechanics that chaos is also the order of the day at the subatomic level. At this very small scale, we can no longer make precise predictions about how a particle like an electron will move. Instead, we must represent its motion as a set of probabilities. (For more on the origins, principles, and weirdness of quantum mechanics, see Physics Girl's video on "The Ultraviolet Catastrophe" below.)
As the temperature is lowered, however, electrons slow down. At low enough temperature (below a so-called critical temperature, abbreviated Tc), electrons are constrained and form exotic phases that exhibit long-range order, or repeating patterns. One of the major goals of this research is to figure out the patterns that electrons form in these exotic phases, and how these patterns determine the properties of a material.
The exotic phases in which electrons organize at low temperatures are interesting because they may exhibit novel behaviors and unexpected properties, like new forms of superconductivity and magnetism---and because, at the quantum level, nothing is weirder than order.
Check out Physics Girl's exploration of quantum mechanics!