Recent research has demystified high-critical-temperature superconductors, identifying their unique "exotic metallic" state and a key quantum critical point. This discovery, the result of a collaborative effort and extensive experimentation, is an important step towards advanced superconducting and sustainable technologies, helping to achieve a greener future.
A research report just published in Nature Communications by researchers from the Politecnico di Milano, Chalmers University of Technology Gothenburg and Sapienza University of Rome reveals one of the many mysteries of high-critical-temperature copper-based superconductors: Even above the critical temperature, they are special and behave like "strange" metals. This means that their resistance changes with temperature differently than regular metals.
This research hints at the existence of a quantum critical point associated with "exotic metals".
Exotic metal behavior and quantum critical points
"Quantum critical point means that under certain conditions, the properties of a material will mutate entirely due to quantum effects." Riccardo Arpaia, a researcher at the Department of Microtechnology and Nanoscience at Chalmers University and the lead author of this study, commented: "Just like ice melts and becomes liquid due to microscopic temperature effects at zero degrees Celsius, copper oxide will also become a 'strange' metal due to quantum charge fluctuations."
The research is based on X-ray scattering experiments performed at the European synchrotron ESRF and the British synchrotron DLS. These experiments revealed the effect of charge density fluctuations on the resistance of copper oxide, which makes copper oxide "weird". Systematic measurements of the changes in the energy of these fluctuations determined the minimum value of the charge carrier density: the quantum critical point.
Impact and future directions
"This is the result of more than five years of work. We used a technology called RIXS, developed mainly by us at the Politecnico di Milano. Through extensive measurement campaigns and new data analysis methods, we demonstrated the existence of quantum critical points." Giacomo Ghiringhelli, professor at the Department of Physics at Politecnico di Milano and research coordinator, added: "A better understanding of copper oxides will help to design better materials with higher critical temperatures, making them easier to exploit in future technologies."
Sergio Caprara, together with his colleagues at the Department of Physics at the University of Rome Sapienza, theorized that charge fluctuations play a key role in copper oxides. He declared: "This discovery is an important advance in understanding not only the anomalous properties of the metallic state of copper oxides, but also the still obscure mechanisms behind high-temperature superconductivity."
Reference: DOI:10.1038/s41467-023-42961-5
Compiled source: ScitechDaily