Scientists have long sought to unravel the mysteries of strange metals — materials that defy conventional rules of electricity and magnetism. Now, a team of physicists at Rice University has made a breakthrough in this area using a tool from quantum information science. Their study, published recently in Nature Communications, reveals that electrons in strange metals become more entangled at a crucial tipping point, shedding new light on the behavior of these enigmatic materials. The discovery could pave the way for advances in superconductors with the potential to transform energy use in the future.
Unlike conventional metals such as copper or gold that have well-understood electrical properties, strange metals behave in much more complex ways, making their inner workings beyond the realm of textbook description. Led by Qimiao Si, the Harry C. and Olga K. Wiess Professor of Physics and Astronomy, the research team turned to quantum Fisher information (QFI), a concept from quantum metrology used to measure how electron interactions evolve under extreme conditions, to find answers. Their research shows that electron entanglement, a fundamental quantum phenomenon, peaks at a quantum critical point: the transition between two states of matter.
“Our findings reveal that strange metals exhibit a unique entanglement pattern, which offers a new lens to understand their exotic behavior,” Si said. “By leveraging quantum information theory, we are uncovering deep quantum correlations that were previously inaccessible.”
A new way to study strange metals
In most metals, electrons move in an orderly fashion, following well-established laws of physics. Strange metals, however, break these rules, showing unusual resistance to electricity and behaving in unusual ways at very low temperatures. To explore this puzzle, the researchers focused on a theoretical model called the Kondo lattice, which describes how magnetic moments interact with surrounding electrons.
At a critical transition point, these interactions become so intense that the fundamental building blocks of electrical behavior, known as quasiparticles, vanish. Using QFI, the researchers tracked the origin of this quasiparticle loss to how electron spins become entangled, finding that entanglement reaches its peak precisely at this quantum critical point.
This novel approach applies QFI, primarily used in quantum information and precision measurements, to the study of metals.
“By integrating quantum information science with condensed matter physics, we are pivoting in a new direction in materials research,” Si said.
Possible path to more efficient energy
The researchers’ theoretical calculations unexpectedly matched real-world experimental data, specifically aligning with results from inelastic neutron scattering, a technique used to probe materials at the atomic level. This connection reinforces the idea that quantum entanglement plays a fundamental role in the behavior of strange metals.
Understanding strange metals is more than just an academic challenge; it could have significant technological benefits. These materials share a close connection with high-temperature superconductors, which have the potential to transmit electricity without energy loss. Unlocking their properties could revolutionize power grids, making energy transmission more efficient.
The study also demonstrates how quantum information tools can be applied to other exotic materials. Strange metals could play a role in future quantum technologies, where enhanced entanglement is a valuable resource. The research provides a new framework for characterizing these complex materials by showing when entanglement peaks.
The research team included Rice’s Yuan Fang, Yiming Wang, Mounica Mahankali and Lei Chen along with Haoyu Hu of the Donostia International Physics Center and Silke Paschen of the Vienna University of Technology. Their work was supported by the National Science Foundation, the Air Force Office of Scientific Research, the Robert A. Welch Foundation and the Vannevar Bush Faculty Fellowship program.