A recent study explores how quantum critical metals defy traditional physics at low temperatures.
The research uncovers that these metals undergo dramatic shifts at quantum critical points, offering valuable insights that could advance the development of high-temperature superconductors.
Exploring the Mysteries of Quantum Critical Metals
A recent study led by Rice University physicist Qimiao Si sheds light on the unconventional behavior of quantum critical metals—materials that break traditional physics laws at low temperatures. Published on December 9 in Nature Physics, the research investigates quantum critical points (QCPs), where materials exist in a delicate state between two distinct conditions, such as magnetic and nonmagnetic. These findings help explain the unique properties of these metals and provide valuable insights for developing high-temperature superconductors, which can conduct electricity without resistance at elevated temperatures.
Understanding Quantum Criticality and Strange Metals
At the core of the study is quantum criticality, a state where materials are highly sensitive to quantum fluctuations—small disturbances that affect electron behavior. While most metals follow established physical laws, quantum critical metals defy these expectations by exhibiting unusual, collective behaviors that have baffled scientists for years. These metals are often referred to as "strange metals."
The Role of Quasiparticles in Quantum Metals
“We explore how quasiparticles lose their identity in strange metals at quantum critical points, leading to unique properties that challenge conventional theories,” explained Si, the Harry C. and Olga K. Wiess Professor of Physics and Astronomy and director of Rice’s Extreme Quantum Materials Alliance.
Quasiparticles, which represent the collective behavior of electrons behaving like individual particles, are vital for energy and information transfer in materials. However, at QCPs, quasiparticles vanish due to a phenomenon called Kondo destruction, where magnetic moments in the material stop interacting with electrons, drastically altering the metal’s electronic structure. This change is visible in the Fermi surface—a map of possible electron states—where a sudden shift occurs when the material crosses the QCP, transforming its properties.
Exploring Universal Patterns Across Materials
The study goes beyond heavy fermion metals—materials with unusually heavy electrons—to include copper oxides and organic compounds. All these strange metals show behaviors that contradict the traditional Fermi liquid theory, which describes electron motion in most metals. Instead, their properties appear to align with fundamental constants like Planck’s constant, which governs the quantum relationship between energy and frequency.
Implications for Advanced Superconductors
One key discovery is dynamical Planckian scaling, where the temperature-dependent properties of these materials mimic universal phenomena, such as cosmic microwave background radiation and black body radiation, which governs star behavior. This insight reveals a shared organizational pattern across quantum critical materials, helping to inform the development of advanced superconductors.
Quantum Transitions in New Materials
The findings also extend to other quantum materials, including iron-based superconductors and those with complex lattice structures. For example, CePdAl, a compound where two competing forces—the Kondo effect and RKKY interactions—determine its electronic behavior, has been examined. By understanding how these forces shape materials at QCPs, scientists aim to unravel similar phenomena in other correlated materials, where complex interelectronic interactions play a major role.
