For many years, physicists have been perplexed by a peculiar phenomenon that occurs in a class of superconducting materials known as “strange metals.” These materials exhibit a high scattering rate of electrons, which is influenced by temperature. Understanding the cause and nature of this phenomenon could provide valuable insights into various quantum material puzzles, including the long-sought-after high-temperature superconductivity.
In a recent breakthrough, a team of international researchers, including physicists from Cornell University, has shed light on the microscopic origins of “Planckian” scattering in a compound called PdCrO2. The scientists compared PdCrO2 with its nearly identical counterpart, PdCoO2, to unravel the mysteries behind this type of scattering.
Planckian scattering refers to the rate at which electrons collide with imperfections within the material and with each other. Surprisingly, this scattering rate increases linearly with temperature. The researchers provided a quantitatively accurate description of the origin of Planckian scattering in strongly interacting metals, marking a significant advancement in the field.
Decoding Planckian Scattering in PdCrO2
The research paper titled “T-linear Resistivity From Magneto-Elastic Scattering: Application to PdCrO2” published in Proceedings of the National Academy of Sciences (PNAS) presents the team’s findings. Debanjan Chowdhury, an assistant professor of physics at Cornell and co-author of the paper, explained that in many strange metals, the characteristic time between electron collisions is determined by Planck’s constant and temperature.
The team’s motivation was to identify a material with accurately known properties to develop a microscopic theory for the origin of Planckian scattering times. PdCrO2, a magnetic “delafossite,” emerged as the material of choice. It serves as a paradigmatic example of an interesting correlated material with two species of electrons: one set that conducts electricity freely, and another set that exhibits magnetism.
The Role of Electron Magnetism
The key to understanding Planckian scattering in PdCrO2 lies in its electron magnetism. PdCrO2, unlike its sister compound PdCoO2, displays electron magnetism. However, magnetism alone is not sufficient to explain the origin of Planckian timescales. The researchers discovered an unexpected cooperative process in PdCrO2 in which electrons interact simultaneously with the crystal’s vibrations and localized spins that constitute magnetism.
“This previously ignored interaction plays a dominant role, and by altering one of these ingredients, we can drive entirely new phenomena,” said Juan Felipe Mendez Valderrama, a doctoral student in physics and co-lead author of the study.
Achieving Fundamental Insights
The joint theory and experiment collaboration between researchers from Cornell, the Weizmann Institute of Science, the Max Planck Institute, and the University of St. Andrews resulted in a comprehensive understanding of Planckian scattering in strange metals. Erez Berg, Elina Zhakina, and Andrew P. MacKenzie are co-authors on this groundbreaking collaboration.
Chowdhury and Berg, long-time collaborators, combined their ideas to solve the experimental puzzle during a summer workshop at the Aspen Center for Physics in 2022. The experimental study titled “Investigation of Planckian Behavior in a High-Conductivity Oxide: PdCrO2” also supports the theory proposed in the research paper.
Chowdhury emphasized the significance of this study in identifying an overlooked source of scattering for electrons in delafossite materials. While the focus was on PdCrO2, the implications extend to a broader range of materials with potentially complex structures. The newfound understanding of Planckian timescales in electrical transport could pave the way for fundamental insights into a larger class of materials.
The quest to unravel the mysteries of Planckian scattering in strange metals has taken a momentous step forward with the study of PdCrO2. By elucidating the microscopic origins of this phenomenon, scientists have laid the groundwork for a more profound comprehension of high-temperature superconductivity and other quantum material puzzles. The future holds immense potential for the discovery of new candidate materials and the emergence of entirely new phenomena by altering the fundamental interactions at play.
Leave a Reply