Polimi experiment uncovers new property in superconductors

The study published in Science shines a new light on cuprates and their characteristics

A study was published in the prestigious periodical Science concerning the results of an experiment carried out by the European Synchrotron ESRF alongside the Politecnico di Milano, the National Research Council, the Sapienza University in Rome and the Chalmers University of Technology in Gothenburg, which has uncovered a new property with regards to cuprates, so-called high-temperature superconductors.

Superconductivity has the potential to reduce all energy waste involved in transporting energy from power plants to our homes to zero. However, in order to achieve this, the wiring needs to be cooled to such low temperatures that for now it is uneconomical to use superconductors on a large scale: for this reason, laboratories across the world are looking for new superconducting materials that can work at less prohibitive temperatures.

High hopes have been placed in cuprates, composites of copper and oxygen also referred to as high-temperature superconductors, which are currently at the centre of the research efforts of the entire scientific community.

An experiment conducted at the ESRF (European Synchrotron Radiation Facility) in Grenoble by the Physics Department of the Politecnico di Milano has uncovered a new property of these materials: the presence, that is, of a variety of charge density waves, referred to as dynamic charge density fluctuations.

These fluctuations seem to not interfere with superconductivity; instead, they influence the electrical resistance in the material’s so-called ‘normal’ state, meaning at temperatures above the critical temperature for superconductivity. Knowing about these charge fluctuations alone does not solve the main mystery, that of superconductivity; however, it explains another odd behaviour of cuprates, that is, the fact that they demonstrate an electrical resistance that is different from that of conventional metals. Furthermore, this new “ingredient” could turn out to be decisive in explaining superconductivity, although for that we will have to wait for future studies.

Already in 2012 it was discovered that in many cases superconductivity in cuprates is contrasted by so-called charge density waves, which partially impede the resistance-less movement of electrons in cuprates, albeit not stopping them entirely: to make progress in what we know about such special materials is key to achieving the production of superconductors that can work at or close to room temperature, one of today’s most crucial technological and scientific challenges.

The experiment that made this observation possible was carried out at the European Synchrotron ESRF by means of the RIXS method, which consists of analysing the prevalent directions taken by dispersed X rays originating from the material under observation.

Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor.
By 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, G. Ghiringhelli
Science 365, 30 August 2019 : 906 (2019)

Illustration: Yen Strandqvist/Chalmers