Using precision techniques for making superconducting thin films layer-by-layer, physicists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have identified a single layer responsible for one such material's ability to become superconducting, i.e., carry electrical current with no energy loss.
The technique, described in the October 30, 2009, issue of Science, could be used to engineer ultrathin films with "tunable" superconductivity for higher-efficiency electronic devices.
"We wanted to answer a fundamental question about such films," said Brookhaven physicist and the group leader Ivan Bozovic. "Namely: How thin can the film be and still retain high-temperature superconductivity?"
The thinner the material (and the higher its transition temperature to a superconductor), the greater its potential for applications where the superconductivity can be controlled by an external electric field. "This type of control is difficult to achieve with thicker films, because an electric field does not penetrate into metals more than a nanometer or so," Bozovic explained.
To explore the limits of thinness, Bozovic's group synthesized a series of films based on the high-temperature superconducting cuprates (copper-oxides) — materials that carry current with no energy loss when cooled below a certain transition temperature (Tc). Since zinc is known to suppress the superconductivity in these materials, the scientists systematically substituted a small amount of zinc into each of the copper-oxide layers. Any layer where the zinc's presence had a suppressing effect would be clearly identified as essential to superconductivity in the film.
"Our measurements showed that the zinc doping had essentially no effect, except when placed in a single, well-defined layer. When the zinc was in that layer, the superconductivity was dramatically suppressed," Bozovic said.
The material studied by Bozovic's team was unusual in that it consists of layers of two materials, one metallic and one insulating, that are not superconductors on their own, but rather exhibit superconductivity at the interface between them [see http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=822].
The layer identified as essential to the superconductivity by the zinc-substitution experiment represents the second copper-oxide layer away from the interface. The scientists found that the presence of zinc had no effect on the transition temperature at which superconductivity sets in, about 32 kelvin (-241 Celsius), except when placed in that particular layer. In the latter case, the scientists observed a dramatic drop in the transition temperature to 18 kelvin (-255 Celsius). The reduction in transition temperature provides a clear indication that that particular layer is the "hot" one responsible for the relatively high temperature at which superconductivity normally sets in for this material.
"We now have a clean experimental proof that high-temperature superconductivity can exist, undiminished, in a single copper-oxide layer," Bozovic said. "This piece of information gives important input to our theoretical understanding of this phenomenon."
Bozovic explained that, in the material he studied, the electrons required for superconductivity actually come from the metallic material below the interface. They leak into the insulating material above the interface and achieve the critical level in that second copper-oxide layer.
But in principle, he says, there are other ways to achieve the same concentration of electrons in that single layer, for example, by doping achieved by applying electric fields. That would result in high-temperature superconductivity in a single copper-oxide layer measuring just 0.66 nanometers.
From a practical viewpoint, this discovery opens a path toward the fabrication of electronic devices with modulated, or tunable, superconducting properties which can be controlled by electric or magnetic fields.
"Electronic devices already consume a large fraction of our electricity usage — and this is growing fast." Bozovic continued. "Clearly, we will need less-power hungry electronics in the future." Superconductors, which operate without energy loss — particularly those that operate at warmer, more-practical temperatures — may be one way to go.
Bozovic's layer-by-layer synthesis method and ability to strategically alter individual layers' composition might also be used to explore and possibly control other electronic phenomena and properties that emerge at the interfaces between layered materials.
This research was funded by the DOE Office of Science.
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 of 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.
Failures in power grids: Dynamically induced cascades
25.05.2018 | Technische Universität Dresden
Beyond the limits of conventional electronics: stable organic molecular nanowires
24.05.2018 | Tokyo Institute of Technology
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences