The modern world -- with its ubiquitous electronic devices and electrical power -- can trace its lineage directly to the discovery, less than two centuries ago, of the link between electricity and magnetism. But while engineers have harnessed electromagnetic forces on a global scale, physicists still struggle to describe the dance between electrons that creates magnetic fields.
Two theoretical physicists from Rice University are reporting initial success in that area in a new paper in the Proceedings of the National Academy of Sciences. Their new conceptual model, which was created to learn more about the quantum quirks of high-temperature superconductors and other high-tech materials, has also proven useful in describing the origins of ferromagnetism -- the everyday "magnetism" of compass needles and refrigerator magnets.
"As a theorist, you strive to have exact solutions, and even though our new model is purely theoretical, it does produce results that match what's observed in the real world," said Rice physicist Qimiao Si, the lead author of the paper. "In that sense, it is reassuring to have designed a model system in which ferromagnetism is allowed."
Ferromagnets are what most people think of as magnets. They're the permanently magnetic materials that keep notes stuck to refrigerators the world over. Scientists have long understood the large-scale workings of ferromagnets, which can be described theoretically from a coarse-grained perspective. But at a deeper, fine-grained level -- down at the scale of atoms and electrons -- the origins of ferromagnetism remain fuzzy.
"When we started on this project, we were aware of the surprising lack of theoretical progress that had been made on metallic ferromagnetism," Si said. "Even a seemingly simple question, like why an everyday refrigerator magnet forms out of electrons that interact with each other, has no rigorous answer."
Si and graduate student Seiji Yamamo
|Contact: David Ruth|