A step towards more sustainable superconductors

Researchers at Chalmers University of Technology in Sweden have unveiled an important mystery in cuprates, a high-temperature superconductor that has evaded researchers for decades. The discovery could advance superconductor research and pave the way for a greener future, as superconductors have the potential to provide 1000 times more energy-efficient devices.

The researchers used a spectrometer, which provides insights into the material electronic and structural properties at the atomic level by analysing the X-rays scattered from the material. Using this method, they were able to detect charge fluctuations in cuprates and confirm the existence of a quantum critical point. Superconducting materials make it possible to transfer electrical energy with zero resistance and high efficiency — as opposed to conventional conducting materials through which energy is partially lost as heat in the process. However, most superconducting materials can only operate at low temperatures, approximately -269°C, which in turn requires a lot of energy and makes them difficult to apply in practice.

Cuprates, a copper-oxide material that conducts electricity with zero resistance at temperatures above that of normal superconductors (approximately -140°C), are an exception in the world of superconducting materials. 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 have not been able to explain why.

Now, in an important step towards the development of room-temperature superconductors, researchers have unveiled the existence of a quantum critical point connected to the phase called “strange metal” — a longstanding theory in the field that this research has strengthened. Riccardo Arpaia, lead author of the study published in Nature Communications, said the discovery represents an advance in understanding not only the anomalous metallic state properties of cuprates, but also the obscure mechanisms underlying high-temperature superconductivity.

The X-ray scattering experiments conducted as part of the research revealed 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.

Giacomo Ghiringhelli, coordinator of the research in collaboration with Chalmers, said the researchers used numerous measurement campaigns and new data analysis methods 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, [that are therefore easier to exploit] in tomorrow’s technologies,” Ghiringhelli said.

Image credit: Chalmers University of Technology.