Superconducting materials have long intrigued physicists due to their unique quantum properties. One particular phenomenon, known as Planckian scattering, has puzzled scientists for years. Planckian scattering refers to the way electrons in certain unconventional metals scatter at high rates, which can be influenced by temperature. Understanding the origin of this scattering could provide crucial insight into various quantum material puzzles, including the elusive high-temperature superconductivity. In two groundbreaking papers, a team of international researchers, including physicists from Cornell University, delves into the microscopic explanation of Planckian scattering in the compound PdCrO2. By comparing it with its “sister” compound PdCoO2, the researchers shed light on the mysterious scattering rate and offer a quantitatively accurate description of its origin.
Many strange metals exhibit a characteristic time between electron collisions, both with each other and any imperfections they encounter in their path. This characteristic time is influenced by Planck’s constant and temperature. Notably, the majority of high-temperature superconductors demonstrate this property when heated above their superconducting temperature. Thus, scientists have long believed that unraveling the common thread across these materials and understanding the universal Planckian time scale could hold the key to understanding high-temperature superconductivity.
To tackle the challenge of understanding Planckian scattering, the team focused on a simpler yet well-characterized material called PdCrO2. This compound belongs to the family of magnetic “delafossite” compounds, which are chromium oxide minerals. PdCrO2 serves as an exemplary correlated material with two species of electrons: mobile electrons that conduct electricity freely and immobile electrons displaying magnetism. The researchers discovered that the electron magnetism in PdCrO2 is a crucial factor contributing to Planckian electrical transport. In contrast, the sister compound PdCoO2, which is structurally similar but lacks magnetism, does not exhibit Planckian behavior.
While magnetism plays a role in the origin of Planckian scattering, it is not the sole explanation. The researchers found that an unexpected cooperative process occurs in PdCrO2, where electrons interact simultaneously with the crystal’s vibrations and the localized spins – the fundamental building blocks of magnetism. This previously overlooked interaction between electrons and vibrations sheds new light on the mysterious Planckian timescales. By identifying this cooperative process, scientists can now explore other materials where this interaction could play a dominant role. Manipulating these ingredients could potentially give rise to entirely new phenomena and expand our understanding of quantum materials.
The groundbreaking research is the result of a collaborative effort between scientists from Cornell University, the Weizmann Institute of Science in Israel, the Max Planck Institute, and the University of St. Andrews. The collaboration was sparked when Debanjan Chowdhury of Cornell and Erez Berg of the Weizmann Institute realized they shared similar ideas for solving the experimental puzzle during a summer workshop. Their joint theory and experiment collaboration paved the way for a comprehensive understanding of Planckian scattering in PdCrO2.
The quest for high-temperature superconductivity is of paramount importance in the field of condensed matter physics. The ability to achieve superconductivity at higher temperatures would revolutionize electrical energy transfer, leading to highly efficient energy use. However, many superconducting materials present significant theoretical challenges in understanding and modeling their behaviors. By focusing on the simpler and well-characterized compound PdCrO2, the researchers hope to lay the groundwork for a more comprehensive theory that can be applied to more complex materials. This newfound understanding of Planckian scattering opens the door to fundamental insights into a broader class of materials where electrical transport exhibits the mysterious Planckian timescale.
The recent breakthroughs in understanding Planckian scattering in superconducting materials, particularly the compound PdCrO2, open up new avenues for research and experimentation. By identifying the cooperative process between electron-vibration interactions and localized spins, scientists can now explore the possibility of harnessing this interaction to induce novel phenomena in other materials. This research not only sheds light on the enigmatic nature of quantum materials but also brings us one step closer to unlocking the full potential of high-temperature superconductivity. With continued collaboration and exploration, scientists may eventually solve the puzzles surrounding Planckian scattering and pave the way for transformative advancements in energy transfer and quantum technology.
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