Strange metal discovery paves way for sustainable superconductors

By using a spectrometer, which provides insights into the material electronic and structural properties at the atomic level by analyzing the X-rays scattered from the material, the researchers were able to detect charge fluctuations in cuprates and confirm the existence of a quantum critical point. Developed in collaboration with Politecnico di Milano, the spectrometer at the European Synchrotron Radiation Facility in Grenoble, named ERIXS, holds the world record for energy resolution.

With the potential to provide 1000 times more energy efficient devices, the quest for a superconductor capable of operating at room temperature is one of the holy grails in physics. Researchers at Chalmers University of Technology in Sweden, Politecnico di Milano and The Sapienza University of Rome have now unveiled an important mystery in cuprates, a high-temperature superconductor that has been evading researchers for decades. The discovery is now believed to advance superconductor research and pave the way for a greener future.  

Superconducting materials make it possible to transfer electrical energy with zero resistance and 100 percent efficiency - as opposed to conventional conducting materials through which energy is partially lost as heat in the process. However, most superconducting materials today can only operate at very low temperatures of roughly – 269 degrees Celsius, which in turn requires a lot of energy and makes them difficult to apply in practice.

A mysterious exception in the world of superconducting materials is “cuprates”: a “strange” copper-oxide material that conducts electricity with zero resistance at temperatures far above that of normal superconductors, up to roughly – 140 degrees Celsius Although it’s a known fact that the electrical resistance in cuprates changes with temperature in a different way than in normal metals, researchers still haven’t been able to explain why.

Now, researchers from Chalmers University of Technology, Politecnico di Milano and The Sapienza University of Rome have succeeded in solving one important mystery of this high-critical-temperature superconductor. The discovery is an important step in the quest for room-temperature superconductors and is believed to pave the way for sustainable technologies and contribute to a greener future. 

“This discovery represents an important advance in understanding not only the anomalous metallic state properties of cuprates, but also the still obscure mechanisms underlying high-temperature superconductivity,” says Riccardo Arpaia, lead author and researcher at Quantum Device Physics at Chalmers University of Technology, who has been coordinating the study together with Politecnico di Milano.

Supporting the existence of quantum critical point

In the study, published in Nature Communications, the researchers managed to unveil the existence of a quantum critical point connected to the phase called "strange metal" – a long standing theory in the field that this research has strengthened. 

The research is based on X-ray scattering experiments conducted at the European Synchrotron ESRF and at the British synchrotron DLS. They reveal the existence of charge density fluctuations affecting the electrical resistance of cuprates in such a way as to make them "strange". The systematic measurement of how the energy of these fluctuations varies allowed researchers to identify the value of the charge carrier density at which this energy is minimum: the quantum critical point.
“Thanks to numerous measurement campaigns and to 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 even better materials, with higher critical temperatures, and therefore easier to exploit in tomorrow's technologies," says Giacomo Ghiringhelli, Professor at the Physics Department of Politecnico di Milano and coordinator of the research in collaboration with Chalmers.

Read more about the study:

Signature of quantum criticality in cuprates by charge density fluctuations

For more information, please contact:

Riccardo Arpaia, researcher Quantum Device Physics, Department of Microtechnology and Nanoscience at Chalmers University of Technology, Sweden, +46 31 772 18 69, riccardo.arpaia@chalmers.se

Media Relations, Politecnico di Milano
Francesca Pierangeli, +39 02 2399 2441, relazionimedia@polimi.it

Karin Wik
Press officer
+46-078 864835
karin.wik@chalmers.se

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