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Breaking the Surface 2008

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fall / Winter 2008 19 Dr. Andrea Damascelli is accustomed to facing the unimaginable. An expert in nanoscience, a field of applied science that seeks to control matter on an atomic and molecular scale, he routinely peers into a world where structures are between 100 and 1,000 times smaller than what scientists are traditionally familiar with. As Canada Research Chair in Electronic Structure of Solids and Associate Professor at UBC Vancouver’s Department of Physics and Astronomy, Damascelli’s research on harnessing the power of high- temperature superconductors and quantum materials is exploring possibilities that few thought were possible – and it is offering the promise of a widespread technological revolution. Conventional superconductors are materials that offer no resistance to the flow of electricity at temperatures reaching absolute zero (-273.15°C). These materials are commonly used in medical imaging machines, lossless power lines and in the development of next-generation quantum computing and information processing. However, their potential has not yet been fully exploited because their topmost surface layers take on different properties from the rest of the material, which provides a critical barrier to their application in functional devices and makes them a difficult subject to study. Despite these obstacles, Damascelli and his team have developed a way to understand and control how electrons behave on the surface of high-temperature superconductors, a breakthrough that is expected to take superconductor research to the next level. “Today, we realize that the thin surface layer of material is really a new playground to work with,” says Damascelli. “Actively manipulating the surface is a better way to control the physics than just hoping nature does what you would like it to do.” The seminal discovery came following experiments conducted at UBC and the Advanced Light Source synchrotron at Berkeley Lab. Synchrotrons, such as at the Canadian Light Source in Saskatoon, are large-scale particle accelerators in which electrons traveling at nearly the speed of light generate the most brilliant light available to scientists. Damascelli and his team’s groundbreaking experiment involves using samples of yttrium-barium-copper oxide, which are widely considered to be the purest high-temperature superconductors and were produced locally by another team of UBC researchers. Firstly, in order to avoid contamination, atomically clean sample surfaces are generated in a stainless steel chamber subject to “outer space” vacuum conditions. Then, potassium atoms are evaporated onto the sample’s surface, unleashing additional electrons on the surface. Finally, ultraviolet light from the synchrotron source is shone on the sample, where it is absorbed by the electrons. The electrons are then expelled from the surface in a way that can be measured by scientists. Damascelli explains: “What we discovered is the number of electrons at the surface is different than inside the sample, which makes the physical properties very, very different. Because of this, we had to find a trick to bring the electrons back to where they are supposed to be and precisely control their number. Using light to emit electrons from a material, we can study those electrons in a vacuum and use energy and momentum conservation laws to infer their properties inside the solid. For instance, we can really study the motion of electrons inside the solid, which defines the electronic properties of the material.” According to Damascelli, the significance of this technique is that scientists are now able to manipulate the number of electrons on the superconductor’s surface in an effort to enhance the material’s potential for applications. While research at this stage is primarily aimed at understanding electron behaviour, the impact of this discovery is expected to have a ripple effect on the development of new technologies that hinge on utilizing extremely thin layers of materials, particularly in the field of electronics and computing. “Material surfaces and interfaces can exhibit very exotic properties; if you can control them, then you can really get into new things,” says Damascelli. “Quantum materials are now a much bigger class of systems with many more spectacular properties. You can imagine the technology that would come out of this could be groundbreaking in many ways. The simplest examples are lossless power lines and high-efficiency fuel cells. More significantly, we’re trying to come up with new electronic materials whose functionality is defined by quantum mechanical interactions and whose application could strongly impact the quality of everyday life.” Dr. Andrea Damascelli’s research is funded by the Canada Foundation for Innovation (CFI) and the Natural Sciences and Engineering Research Council of Canada (NSERC). Under Damascelli’s leadership, future studies into superconductor and quantum material technology will be conducted at the Quantum Materials Spectroscopy Centre at the Canadian Light Source in Saskatoon. B r e a k i n g  t h e  s u r f a c e andrea daMasceLLi is Looking to usher in a neW era of quantuM coMputing With a groundBreaking technique that defies aLL nanotechnoLogy research to date “ We had to find a trick to bring the electrons back to where they are supposed to be.” The Fermi surface of a high-temperature superconductor as revealed by angle-resolved photoemission spectroscopy. Photo > Andrea Damascelli


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