In a groundbreaking study, Rice University physicist Qimiao Si and his team have shed new light on the mysterious behavior of quantum critical metals. These materials, known as “strange metals,” defy the usual rules of physics at low temperatures. Published in Nature Physics, the research explores quantum critical points (QCPs), where materials hover between two distinct states, such as being magnetic or nonmagnetic.
The findings help explain the unique properties of these metals and offer insights into high-temperature superconductors, which conduct electricity without resistance at relatively high temperatures. At the heart of the study is quantum criticality, a state where materials become extremely sensitive to quantum fluctuations. While most metals follow well-established physical laws, quantum critical metals display unusual and collective behaviors that have puzzled scientists for decades.
“Our work dives into how quasiparticles lose their identity in strange metals at these quantum critical points, which leads to unique properties that defy traditional theories,” said Si, the Harry C. and Olga K. Wiess Professor of Physics and Astronomy and director of Rice’s Extreme Quantum Materials Alliance.
Quasiparticles, representing the collective behavior of electrons acting like individual particles, play a crucial role in energy and information transfer in materials. However, at QCPs, these quasiparticles vanish in a phenomenon known as Kondo destruction.
Quantum criticality in strange metals
This change is evident in the Fermi surface, a map of possible electron states within the material. As the system crosses the QCP, the Fermi surface abruptly shifts, significantly altering the material’s properties. The study extends beyond heavy fermion metals to include copper oxides and certain organic compounds.
All of these strange metals exhibit behaviors that defy traditional Fermi liquid theory, a framework used to describe electron motion in most metals. Instead, their properties align with fundamental constants such as Planck’s constant, governing the quantum relationship between energy and frequency. The researchers identified a condition called dynamical Planckian scaling, where the temperature dependence of electronic properties mirrors universal phenomena like cosmic microwave background radiation and black body radiation, which approximates the behavior of stars.
This discovery underscores a shared organizational pattern across various quantum critical materials, offering insights into creating advanced superconductors. The research implications extend to other quantum materials, including iron-based superconductors and those with intricate lattice structures. One example is CePdAl, a compound where the interplay of two competing forces determines its electronic behavior.
By studying these transitions, scientists hope to decode similar phenomena in other correlated materials, where complex inter-electronic relationships dominate. This research, co-authored by Haoyu Hu and Lei Chen from Rice’s Department of Physics and Astronomy, Extreme Quantum Materials Alliance, and Smalley-Curl Institute, was supported by the National Science Foundation, Air Force Office of Scientific Research, Robert A. Welch Foundation, Vannevar Bush Faculty Fellowship, and European Research Council.
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