HOUSTON, Feb. 12, 2007 -- The W.M. Keck Foundation has awarded Rice University $1.4 million to probe one of the most elusive and mysterious areas of modern physics – the bizarre world of high-temperature superconductors, quantum magnets, and other solid-state materials that have "strongly correlated" electrons.
"The past decade has witnessed incredible experimental breakthroughs in both ultracold atomic physics and condensed matter physics," said physicist Randy Hulet, co-director of Rice's Keck Program in Quantum Materials. "We believe Rice has all the pieces in place to make breakthroughs in our understanding of effects that have puzzled physicists for more than 20 years."
Given the past decade's advances in nanoscale fabrication, laser cooling and other technologies, many believe the stage is set for a major leap in our understanding of exotic materials, such as high-temperature superconductors, where the electrons interact so strongly with one another that their actions cannot be explained by simple theories.
Unlike electrons in simple metals, which hardly notice one another, the electrons in high-temperature superconductors and some magnetic materials are intricately linked. Physicists cannot predict how any single electron in the material will act without considering the actions of all of its neighbors. While considerable theoretical efforts have been made, leading to the development of major new concepts, a unified framework remains elusive for the understanding of these strongly correlated electronic materials.
"It's the electron-electron interactions and quantum fluctuations in these classes of materials that both create these great effects and make them so difficult to explain," said program co-director Doug Natelson, a condensed matter experimentalist. "In most solid-state materials, physicists can often get away with ignoring interaction effects because they are overpowered by stronger forces. That's just not possible in these materials." Natelson said tunable models of these materials based on either nanostructures or cold atoms can examine these issues directly.
For example, the advent of laser-cooling technology within the past decade has allowed physicists working at the atomic scale to create a number of elusive states of quantum matter, including Bose-Einstein Condensates, or BECs, which were first predicted by Albert Einstein in the 1920s. Under the new Keck program, Hulet's lab – one of the first in the world to make BECs – is preparing a new apparatus to test the two-dimensional Hubbard model, a theory put forward more than 20 years ago to describe the conduction and magnetic properties of one type of strongly interacting materials, the high-temperature superconductors. Hulet said his apparatus will allow the use of a gas of ultracold atoms in place of the electrons in real materials to fine tune certain properties of the system and provide theorists with data that they couldn't otherwise get from a real material.
Similarly, mobile electrons in “heavy fermion” materials act hundreds of times more massive than those in ordinary metals because of quantum interactions with magnetic atoms. The magnetic atoms also talk to each other. A new experiment in Natelson’s lab will use a single-molecule electronic device as a model of these rich materials. Dialing a voltage on the device will controllably shift the relative importance of the interactions, so that the system may be tuned from a normal metal state into a quantum regime with unusual conducting properties. Studies of this quantum phase transition in real materials have given rise to many open questions, which the model system is uniquely suited to address.
These projects are two of several that the Keck Program will support. In all, eight principle investigators at Rice will participate in the program. These include condensed matter experimentalists Jun Kono and Rui-Rui Du, and ultracold atom experimentalist Tom Killian. Theoretical connections will be made by atomic matter theorist Han Pu and condensed matter theorists Qimiao Si and Carl Bolech.
"Quantum magnetism and strong correlations are subjects in which theory and experiment have always gone hand in hand over the course of studying real condensed matter materials," said Si. "In the Keck program, theory will not only provide the intellectual foundation but will also serve as the intellectual glue."
Hulet and Natelson said Rice is matching Keck's contribution with $1.4 million of its own. They said the lion's share of program funds will pay the salaries of three Keck Postdoctoral Fellows and three graduate students who will focus exclusively on the program's projects.