Researchers from Chalmers University of Technology and Politecnico di Milano have identified a crucial new aspect of charge density modulations in cuprate high critical temperature superconductors. They have identified a new electron wave which could help reveal some of the mysteries about superconducting materials. The findings are published in the journal Science.
High critical temperature superconductors have a variable charge density, meaning that their electrical charge is unevenly distributed. This partly results from what are known as 'charge density waves', which were discovered a few years ago.
But these have only been observed to exist sporadically, under certain conditions. Therefore, they were not believed to be a contributing factor to the materials' superconducting properties.
What the researchers have now discovered, however, is an additional aspect to the variable charge density, which they term "charge density fluctuations". These have been identified as an additional charge modulation, collective and with a shorter correlation length.
They are very pervasive, meaning that compared to the conventional charge density waves, they are present at a much greater range of temperatures, up to room temperature and beyond, and at different levels of oxygen doping.
"These charge density fluctuations could be a crucial ingredient of the highly unconventional room temperature properties of high critical temperature superconductors - something which challenges our common understanding of the charge transport in metals," says Riccardo Arpaia, postdoctoral researcher at the Department of Microtechnology and Nanoscience at Chalmers, who carried out the research.
"One could say the charge density waves, which were already very well known, were just the tip of the iceberg. The charge density fluctuations which we have now identified are like the hidden bulk of the iceberg." says Riccardo Arpaia. "The discoveries were possible thanks to the major developments of synchrotron-based x-ray scattering techniques, and to the quality of the samples we have used."
The samples were fabricated at the Italian National Research Council in Napoli, and in the research group at Chalmers led by Professor Floriana Lombardi.
A further finding of the paper looks at how the charge density fluctuations evolve with the temperature of the material. While the previously-known charge density waves change abruptly as soon as the critical temperature is reached - meaning, dependent on whether the material is in a superconductive state or not, the newly-discovered charge density fluctuations are unaffected by the superconductivity. This indicates that the two characteristics are not 'in competition' with one another. This finding might strengthen the researchers' theory that the charge density fluctuations are the key to explaining the mystery of these materials.
Because superconductors operate at such low temperatures, they require cooling from liquid helium or liquid nitrogen, making them expensive and difficult to use outside of certain commercial applications. But if a superconductor could be made to work closer to room temperature, it could have enormous potential. Therefore, there is a lot of interest in improving our understanding of how this class of superconductors works.
Giacomo Ghiringhelli, Professor of Physics at Politecnico di Milano says about the research: "Since 2012, when charge density waves in cuprates were first observed, their importance had not been disputed - but their role had remained unclear. The newly observed charge density fluctuations appear to be a very general property of these materials, meaning they are likely playing a crucial role in the transport of electric current in cuprates."
Read the article "Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor" in the journal Science.
More information about superconductors
Superconductors are materials which, when exposed to a certain temperature, known as the 'critical temperature', suddenly acquire incredible new properties - chiefly, that they can conduct electrical charge with zero resistance.
Most superconductors currently in commercial use are known as low critical temperature - typically meaning below about -240 degrees Celsius. High critical temperature superconductors meanwhile, are those which exhibit superconducting properties at a somewhat higher temperature - though still hundreds of degrees below zero. The most common type are known as 'cuprates', made from a mixture of copper and oxygen - it was this particular class of superconductors which the researchers investigated.
European collaboration for the research
Riccardo Arpaia, co-lead author of the paper, is a researcher from Chalmers University of Technology who, through the framework of the Swedish Research Council's international postdoc programme, also researches at Politecnico di Milano, in the group of Giacomo Ghiringhelli, who conceived the experiment.
Chalmers and Politecnico di Milano are both members of the IDEA league, an alliance of five leading European technological universities, that aims to encourage and elevate European research in science and technology by sharing academic resources and knowledge.
Experiments were performed at the European Synchrotron Radiation Facility in Grenoble, in collaboration with researchers of the Italian National Research Council (CNR) and of the Sapienza University of Rome.
Resonant inelastic X-ray scattering
The researchers identified the charge density fluctuations through the use of a technique known as resonant inelastic X-ray scattering. RIXS is a spectroscopy technique, where photons (X-ray radiation) get scattered from a material due to interaction with electronic clouds.
RIXS is, as suggested by the name, a resonant technique, since the energy of the incident photons coincides, and hence resonates, with a specific electronic transition (the Cu L3 edge at ?931 eV, in the case illustrated in the paper). This strongly enhances the signal. For this reason, RIXS currently represents the best technique for the detection of weak charge density modulations with particularly short correlation lengths, going even beyond previous limits set by neutron scattering and scanning tunnel microscopy techniques.
The exceptional results presented in this work were made possible by the innovative "ERIXS" instrument realised jointly by the ESRF and the Politecnico di Milano.
For more information, contact:
Department of Microtechnology and Nanoscience
Chalmers University of Technology
+46 31 772 18 69
Joshua Worth | EurekAlert!
New metamaterial morphs into new shapes, taking on new properties
12.09.2019 | California Institute of Technology
Reconfigurable electronics show promise for wearable, implantable devices
10.09.2019 | American Institute of Physics
Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Potsdam (both in Germany) and the University of Toronto (Canada) have pieced together a detailed time-lapse movie revealing all the major steps during the catalytic cycle of an enzyme. Surprisingly, the communication between the protein units is accomplished via a water-network akin to a string telephone. This communication is aligned with a ‘breathing’ motion, that is the expansion and contraction of the protein.
This time-lapse sequence of structures reveals dynamic motions as a fundamental element in the molecular foundations of biology.
Two research teams have succeeded simultaneously in measuring the long-sought Thorium nuclear transition, which enables extremely precise nuclear clocks. TU Wien (Vienna) is part of both teams.
If you want to build the most accurate clock in the world, you need something that "ticks" very fast and extremely precise. In an atomic clock, electrons are...
Researchers from Chalmers University of Technology have demonstrated a detector made from graphene that could revolutionize the sensors used in next-generation space telescopes. The findings were recently published in the scientific journal Nature Astronomy.
Beyond superconductors, there are few materials that can fulfill the requirements needed for making ultra-sensitive and fast terahertz (THz) detectors for...
A supersolid is a state of matter that can be described in simplified terms as being solid and liquid at the same time. In recent years, extensive efforts have been devoted to the detection of this exotic quantum matter. A research team led by Tilman Pfau and Tim Langen at the 5th Institute of Physics of the University of Stuttgart has succeeded in proving experimentally that the long-sought supersolid state of matter exists. The researchers report their results in Nature magazine.
In our everyday lives, we are familiar with matter existing in three different states: solid, liquid, or gas. However, if matter is cooled down to extremely...
A team headed by Prof. Steve Albrecht from the HZB will present a new world-record tandem solar cell at EU PVSEC, the world's largest international photovoltaic and solar energy conference and exhibition, in Marseille, France on September 11, 2019. This tandem solar cell combines the semiconducting materials perovskite and CIGS and achieves a certified efficiency of 23.26 per cent. One reason for this success lies in the cell’s intermediate layer of organic molecules: they self-organise to cover even rough semiconductor surfaces. Two patents have been filed for these layers.
Perovskite-based solar cells have experienced an incredibly rapid increase in efficiency over the last ten years. The combination of perovskites with classical...
10.09.2019 | Event News
04.09.2019 | Event News
29.08.2019 | Event News
13.09.2019 | Earth Sciences
13.09.2019 | Power and Electrical Engineering
13.09.2019 | Power and Electrical Engineering