Charge Fluctuations: A New Property of Superconductors
Superconductivity would allow us to eliminate any waste in the transportation of energy from electricity plants to our houses. However, to achieve this, it would be necessary to cool electrical wiring to such low temperatures that the wide-scale use of superconductors would not be economically feasible. This is why research labs worldwide are working on the identification of new superconductive materials that work at less extreme temperatures. There is great hope in the so-called cuprates, basic compounds of copper and oxygen that are also known as high-temperature superconductors, on which the scientific community is currently focusing. An experiment conducted at the Grenoble ESRF (European Synchrotron Radiation Facility) light source, coordinated by the Milan Polytechnic Department of Physics, together with researchers from the National Research Council Spin Institute, the Sapienza University Department of Physics and the University of Chalmers in Göteborg, revealed a new characteristic of these materials: the presence of a variety of charge density waves referred to as dynamic charge density fluctuations.
The study has been published on Science. These fluctuations do not seem to interfere with superconductivity, instead they influence electrical resistance in the “normal” state (at temperatures higher than the critical superconductive temperature). Knowledge about the presence of these charge fluctuations does not solve the main problem, that of superconductivity. It does, however, allow us to explain another strange characteristic of cuprates: the fact that they have such a different electrical resistance to conventional metals. And this may be decisive to explain superconductivity, although this hypothesis needs to be verified.
Since 2012, we have observed that in many cases the superconductivity of cuprates is contrasted by charge density waves that partially obstruct the movement without resistance of electrons in cuprates, although they do not completely block it. Gaining further understanding of these special materials is fundamental to the future production of superconductors that work at room temperature (or nearly), one of today’s greatest technological and scientific challenges.
The experiment that made these observations possible was conducted at the European ESRF Synchrotron with the RIXS Technique. This allows the analysis of the diffusion of X-rays by the material under study along privileged directions.
"Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor’, R. Arpaia, S. Caprara, R. Fumagalli, G. De Vecchi, Y.Y. Peng, E. Andersson, D. Betto, G. M. De Luca, N. B. Brookes, F. Lombardi, M. Salluzzo, L. Braicovich, C. Di Castro, M. Grilli, and G. Ghiringhelli. Science 30 Aug 2019: Vol. 365, Issue 6456, pp. 906-910 DOI: 10.1126/science.aav1315
Physics Department, Sapienza University of Rome