This simple discovery opens a door to new research that could lead to room-temperature superconductors.
“Cornell has the world’s best, if not the universe’s best scanning tunneling microscope (STM) facility; combining that with a new theoretical idea enabled this discovery,” said Eun-Ah Kim, assistant professor of physics at Cornell and corresponding author of a report published July 15 in the journal Nature.
“We know if you identify the broken symmetries, you are close to understanding how a material works,” said J.C. Séamus Davis, Cornell’s J.D. White Distinguished Professor of Physical Sciences and director of the Center for Emergent Superconductivity at Brookhaven National Laboratory. He said the discovery is analogous to learning that a key to controlling liquid crystals (found in the LCD displays in watches, calculators and computer monitors) was that the molecules can arrange into an asymmetrical state.
Broken symmetries are seen in many materials when they undergo a “phase transition” like that of water freezing into ice, or liquid crystals becoming opaque. A material going into a superconducting state – conducting electricity with zero resistance – is another kind of phase transition.
Superconductivity was first discovered in pure metals cooled very close to absolute zero (-273 degrees Celsius). Ceramic materials called cuprates superconduct at temperatures as “high” as 150 Kelvins (degrees above absolute zero). Cuprates are made up of copper oxide layers alternating with layers of other elements. Each copper oxide layer is a checkerboard sheet formed by repeating an L-shaped unit of one copper and two oxygens, with one oxygen atom to the “north” and the other to the “east” of each copper. The presence of other elements between the copper oxide sheets nudges electrons in the copper oxide sheet around and, at the right combinations of temperature and chemical content, creates a condition for superconductivity.
Davis and his experimental group study these materials using an exceptionally precise STM that can map the location of atoms and energy levels of the electrons around them. In the superconducting phase, an “energy gap” appears – electrons that ought to be in certain energy levels associated with atoms disappear to form “Cooper pairs” that travel without resistance. But above the superconducting temperature there is a range where the energy gap is still seen, but superconductivity is not.
This “pseudogap” phase may extend all the way to room temperature in some materials, so learning to overcome its limitations could lead to room-temperature superconductors.The broken symmetry has been present but hidden in existing data from STM experiments including ones from the Davis group, said Kim, who, with colleagues at Cornell and Binghamton, proposed a new theoretical perspective and mathematical procedure to reveal the broken symmetry from the data.
Previously, Kim said, theorists had focused only on the arrangement of the copper atoms, and experimentalists had been averaging signals over all the oxygen atoms in a sample, rather than comparing “east-west” and “north-south” signals.
Kim said the finding presents “an opportunity for a whole new stage of research. We have a map of this broken symmetry, now we can experimentally study how it affects superconductivity. Further, the importance of oxygen sites for the broken symmetry points to a theoretical model that may explain the mechanism of pseudogap and high Tc [critical temperature] superconductivity.“
The research was supported primarily by the National Science Foundation and Department of Energy. Additional funding was provided by the U.S. Army Research Office and University of British Columbia.
Text written by Bill Steele, Cornell University Chronicle
Blaine Friedlander | Newswise Science News
Large-scale battery storage system in field trial
11.12.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH
New test procedure for developing quick-charging lithium-ion batteries
07.12.2017 | Forschungszentrum Jülich
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong
Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...
An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications
Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...
Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.
The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
11.12.2017 | Physics and Astronomy
11.12.2017 | Earth Sciences
11.12.2017 | Information Technology