New Bodies Electric

The electrons in some materials respond powerfully to each other, appearing to attract or align in unexpected ways. Scientists studying these strongly-correlated quantum systems have continued to reinvent the field through discoveries of new materials, such as novel superconductors, new findings through high-precision experiments, and new connections between seemingly disparate theoretical methods. In August, 113 theoreticians and experimentalists gathered at ICTP for the Workshop on the Principles and Design of Strongly Correlated Electronic Systems.

“We are fascinated by the emergent properties of quantum matter,” said Rutgers physicist Piers Coleman, one of the directors of the workshop. “You might think that since we have the equations of quantum mechanics, we should be able to understand what happens when you put electrons and protons and neutrons together. But remarkably, things don’t always behave as we might have expected.”

For instance, strongly correlated electronic systems undergo unusual transitions in their behaviour with changes in pressure, chemical composition, and magnetic field, called “quantum phase transitions”. In such a transition, an insulator can become a superconductor.

As a material approaches a quantum phase transition, the quantum effects become more and more intense, giving rise to correlations that last infinitely long in time and perhaps stretch out to infinitely long distances in space, Coleman said. These transitions are thought to occur at absolute zero but their effects might still be seen at temperatures as high as 1000 K (727 degrees Celsius). In contrast, the well-studied thermal phase transitions affect behaviour only near the critical point.

“The ideas that explained classical critical points can’t be used on quantum critical points,” he added. “We don’t understand why, actually.”

“Understanding why” is the duty of theorists, who benefit from frequent infusions of experimental data in this field. “There is nothing better than to confront theorists with reality,” Coleman said.

ICTP theoretical physicist Erio Tosatti, another organizer of the workshop, agreed with Coleman.  “Given two things equally beautiful, I have a lot more attraction for something that actually exists,” Tosatti said. But experimentalists should not ignore the benefit of theoretical advances, he added.

“You don’t do a meaningful experiment if you have no background in theory,” Tosatti said. "The experimentalists who participate in this conference get ideas for what to measure, what is important and what is not."

The workshop boasted leading theorists and experimentalists in the field. Laura Greene, a condensed matter physicist from the University of Illinois, Urbana-Champaign, said she enjoyed the broad range of topics covered.

“It’s a giant mosaic,” Greene said. “Everyone is putting their own tiles in. We are starting to see the patterns.”

More details about the workshop can be found here.