These Superconductors Behave Strangely, and Scientists Finally Know Why

Groundbreaking research in superconductivity has revealed new insights into high critical temperature copper-based superconductors. Collaborative efforts discovered the strange behavior of metals in these superconductors and identified a quantum critical point. Extensive X-ray experiments led to this discovery, which holds promise for future technologies and sustainable solutions. Source: SciTechDaily.com

Recent research has uncovered key aspects of superconductors with high critical temperatures, indicating their unique ‘strange metal’ status and an important quantum critical point. This discovery, the result of collaborative efforts and extensive experiments, paved the way for advanced superconducting technologies.

Taking an important step in superconductivity research, the discovery could pave the way for sustainable technologies and contribute to a more environmentally friendly future.

The study was recently published in Communication in Nature by researchers from the Politecnico di Milano, Chalmers University of Technology in Göteborg, and Sapienza University of Rome shed light on one of the many mysteries of high critical temperature copper-based superconductors: even at temperatures above the critical temperature, they are special, behaving like “strange” metals. This means that their electrical resistance changes with temperature differently than normal metals.

The research shows the existence of a quantum critical point connected to the phase called “strange metal.”

Phase Diagram of Cuprates

Phase diagram of cuprates. Credit: Politecnico di Milano

Strange Properties of Metals and Quantum Critical Points

“A quantum critical point indicates certain conditions where a material undergoes a sudden change in its properties due to quantum effects only. Like ice that melts and becomes liquid at zero degrees Celsius due to microscopic temperature effects, cuprates become ‘strange’ metals due to quantum charge fluctuations” commented Riccardo Arpaia, researcher in the Department of Microtechnology and Nanoscience at Chalmers and lead author of study.

The research is based on X-ray scattering experiments carried out at the European Synchrotron ESRF and the British synchrotron DLS. They revealed the existence of charge density fluctuations that affect the electrical resistance of cuprates in a way that makes them “strange.” The systematic measurement of how the energy of these fluctuations is allowed to determine the value of the charge carrier density where this energy is minimum: the quantum critical point.

ERIXS Instrument European Synchrotron ESRF

The ERIXS instrument at the European Synchrotron ESRF in Grenoble. Credit: Politecnico di Milano

Impact and Future Directions

“This is the result of more than five years of work. We use a technique, called RIXS, which we mainly develop at Politecnico di Milano. Thanks to many measurement campaigns and new data analysis methods, we have been able to prove the existence of the quantum critical point. A better understanding of cuprates will guide the design of better materials, with higher critical temperatures, and therefore easier to exploit tomorrow’s technology,” added Giacomo Ghiringhelli, Professor of Physics Department of Politecnico di Milano and coordinator of research.

Sergio Caprara, together with his colleagues at the Department of Physics at the Sapienza University of Rome, developed the theory that assigns charge fluctuations an important role in cuprates. He stated that “This discovery represents a significant advance in understanding not only the anomalous properties of the metallic state of cuprates, but also the unknown mechanisms underlying high-temperature superconductivity .”

Reference: “Signature of quantum criticality in cuprates by charge density fluctuations” by Riccardo Arpaia, Leonardo Martinelli, Marco Moretti Sala, Sergio Caprara, Abhishek Nag, Nicholas B. Brookes, Pietro Camisa, Qizhi Li, Qiang Gao, Xingjiang Zhou, Mirian Garcia -Fernandez, Ke-Jin Zhou, Enrico Schierle, Thilo Bauch, Ying Ying Peng, Carlo Di Castro, Marco Grilli, Floriana Lombardi, Lucio Braicovich and Giacomo Ghiringhelli, 8 November 2023, Communication in Nature.
DOI: 10.1038/s41467-023-42961-5


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