Warmed beyond those frigid conditions, the materials cross a critical temperature threshold and the superconductivity breaks down. But high-temperature superconductors (HTS)—warmer, but still subzero—may have untapped potential because their underlying mechanism remains a mystery.
Unlocking that unknown HTS source and engineering new superconductor configurations could drive that critical temperature high enough to revolutionize energy technology.
Now, scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have discovered an unexpected and anomalous pattern in the behavior of one high-performing class of HTS materials. In the new frontier of interface physics, two non-conducting materials can be layered to produce HTS behavior, with tantalizing and mystifying results. Testing a sample set of unprecedented size—more than 800 distinct, custom-made materials—the researchers found that the critical temperature for superconductivity remained constant across a wide range of atomic compositions.
“Theory predicted that the critical temperature in these interface samples would depend strongly on the electron content, but we saw no such dependence,” said Brookhaven physicist Ivan Bozovic, lead investigator on the new study published online August 4, 2013, in the journal Nature Materials. “We are exploring uncharted territory with unprecedented precision.”
Scientists can tweak the average number of electrons present in HTS films—called the doping level or carrier density—to optimize performance and explore the poorly understood phenomenon. The lanthanum, strontium, copper, and oxygen (LSCO) films used in this study change based on that doping level, transforming into under-doped insulator, a well doped superconductor, or an over-doped and non-superconducting metal. Much HTS research is dedicated to exploring the “just right” regime in the middle, but the ends of the spectrum hold considerable potential.
“Years ago, we discovered something truly remarkable at the interface between an LSCO insulator and an over-doped metal,” Bozovic said. “An unpredicted superconductivity emerged with a significantly enhanced critical temperature of more than 50 Kelvin.”
That temperature may be frosty (-370 degrees Fahrenheit), but the interface threshold is downright balmy compared to traditional superconductors and even 25 percent warmer than single-phase LSCO materials. Faced with this promising puzzle, the Brookhaven Lab team set out to test the many possible atomic configurations of LSCO interface superconductors.
To map the relatively simple phase diagram of water—its journey from solid ice to gaseous vapor—the temperature must be incrementally increased. Leaping up by 10 degrees, for example, would leave considerable gaps and reveal very little about the exact phase transitions or how to harness them.
“To pinpoint the parameters of interface HTS, which is characterized by quantum phase transitions rather than thermal, we tuned the carrier density,” Bozovic said. “So unlike the simple application of heat, we had to alter the atomic composition of our samples.”
Without confirmed theories on interface superconductivity to guide design, each electron configuration must be synthesized and directly tested. And to make matters even more challenging, the Brookhaven collaboration needed hundreds of these precisely tailored LSCO samples.
“When studying complex materials, one needs robust statistics to identify trends—finding what is ubiquitous or intrinsic and filtering out the random and irrelevant,” Bozovic said. “So we fabricated more than 800 samples, each one almost atomically perfect, with subtle changes in the doping level.”
To accomplish this feat, the scientists used a custom-designed atomic layer-by-layer molecular beam epitaxy system (ALL-MBE) at Brookhaven Lab. The MBE group, which Bozovic leads, grew the thin LSCO films inside strictly controlled vacuum chambers. They then lithographically patterned the films—a bit like micrometer-scale printing—into an array of distinct pixels, each with a slightly different chemical composition. The researchers then measured the flow of current against the related doping levels in each pixel to chart the rise and fall of HTS.
“Our technique accelerated the sample testing process by 30 times or more,” Bozovic said. “More importantly, we could vary the doping level in steps one hundred times smaller than in standard methods.”
To the surprise of the Brookhaven scientists, the critical temperature for interface superconductivity in each of the 800 samples stayed constant at about 40 Kelvin. The doping level, even at the optimum levels predicted by theoretical models, did not appear to shift the electro-chemical potential of the HTS materials.
“The results pose a new challenge to HTS theories,” Bozovic said. “This study exemplifies the rich puzzle of interface physics and the other new discoveries that can be made through advanced experimentation.”
Additional collaborators on the research include Jie Wu, Oshiri Pelleg, Anthony Bollinger, Yujie Sun, all of Brookhaven Lab, Mihajlo Vanevic and Zoran Radovic of University of Belgrade, Serbia, and Gregory Boebinger of the National High Magnetic Field Laboratory.
The research was funded by the DOE’s Office of Science, the Serbian Ministry of Science and Education, and the National Science Foundation.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov.
One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
Justin Eure | Newswise
New biomaterial could replace plastic laminates, greatly reduce pollution
21.09.2017 | Penn State
Stopping problem ice -- by cracking it
21.09.2017 | Norwegian University of Science and Technology
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Power and Electrical Engineering
25.09.2017 | Health and Medicine
25.09.2017 | Physics and Astronomy