(Press-News.org) ANN ARBOR--An odd, iridescent material that's puzzled physicists for decades turns out to be an exotic state of matter that could open a new path to quantum computers and other next-generation electronics.
Physicists at the University of Michigan have discovered or confirmed several properties of the compound samarium hexaboride that raise hopes for finding the silicon of the quantum era. They say their results also close the case of how to classify the material--a mystery that has been investigated since the late 1960s.
The researchers provide the first direct evidence that samarium hexaboride, abbreviated SmB6, is a topological insulator. Topological insulators are, to physicists, an exciting class of solids that conduct electricity like a metal across their surface, but block the flow of current like rubber through their interior. They behave in this two-faced way despite that their chemical composition is the same throughout.
The U-M scientists used a technique called torque magnetometry to observe tell-tale oscillations in the material's response to a magnetic field that reveal how electric current moves through it. Their technique also showed that the surface of samarium hexaboride holds rare Dirac electrons, particles with the potential to help researchers overcome one of the biggest hurdles in quantum computing.
These properties are particularly enticing to scientists because SmB6 is considered a strongly correlated material. Its electrons interact more closely with one another than most solids. This helps its interior maintain electricity-blocking behavior.
This deeper understanding of samarium hexaboride raises the possibility that engineers might one day route the flow of electric current in quantum computers like they do on silicon in conventional electronics, said Lu Li, assistant professor of physics in the College of Literature, Science, and the Arts and a co-author of a paper on the findings published in Science.
"Before this, no one had found Dirac electrons in a strongly correlated material," Li said. "We thought strong correlation would hurt them, but now we know it doesn't. While I don't think this material is the answer, now we know that this combination of properties is possible and we can look for other candidates."
The drawback of samarium hexaboride is that the researchers only observed these behaviors at ultracold temperatures.
Quantum computers use particles like atoms or electrons to perform processing and memory tasks. They could offer dramatic increases in computing power due to their ability to carry out scores of calculations at once. Because they could factor numbers much faster than conventional computers, they would greatly improve computer security.
In quantum computers, "qubits" stand in for the 0s and 1s of conventional computers' binary code. While a conventional bit can be either a 0 or a 1, a qubit could be both at the same time--only until you measure it, that is. Measuring a quantum system forces it to pick one state, which eliminates its main advantage.
Dirac electrons, named after the English physicist whose equations describe their behavior, straddle the realms of classical and quantum physics, Li said. Working together with other materials, they could be capable of clumping together into a new kind of qubit that would change the properties of a material in a way that could be measured indirectly, without the qubit sensing it. The qubit could remain in both states.
While these applications are intriguing, the researchers are most enthusiastic about the fundamental science they've uncovered.
"In the science business you have concepts that tell you it should be this or that and when it's two things at once, that's a sign you have something interesting to find," said Jim Allen, an emeritus professor of physics who studied samarium hexaboride for 30 years. "Mysteries are always intriguing to people who do curiosity-driven research."
Allen thought for years that samarium hexaboride must be a flawed insulator that behaved like a metal at low temperatures because of defects and impurities, but he couldn't align that with all of its other properties.
"The prediction several years ago about it being a topological insulator makes a lightbulb go off if you're an old guy like me and you've been living with this stuff your whole life," Allen said.
In 2010, Kai Sun, assistant professor of physics at U-M, led a group that first posited that SmB6 might be a topological insulator. He and Allen were also involved in seminal U-M experiments led by physics professor Cagliyan Kurdak in 2012 that showed indirectly that the hypothesis was correct.
"But the scientific community is always critical," Sun said. "They want very strong evidence. We think this experiment finally provides direct proof of our theory."
INFORMATION:
The paper is titled "Two-dimensional Fermi surfaces in Kondo Insulator SmB6." It was funded by the U.S. Department of Energy and the National Science Foundation. The U-M Mcubed program also provided seed funds for this research.
(MEMPHIS, Tenn. - December 5, 2014) An international research collaborative has determined that a promising anti-malarial compound tricks the immune system to rapidly destroy red blood cells infected with the malaria parasite but leave healthy cells unharmed. St. Jude Children's Research Hospital scientists led the study, which appears in the current online early edition of the Proceedings of the National Academy of Sciences (PNAS).
The compound, (+)-SJ733, was developed from a molecule identified in a previous St. Jude-led study that helped to jumpstart worldwide anti-malarial ...
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Doctor Jordan Santos-Concejero, of the Department of Physical Education and Sport at the UPV/EHU, carried out research the aim of which was to analyse the response of cerebral oxygenation at maximum and progressive rhythms amongst elite Kenyan runners ...
Pretty soon, powering your tablet could be as simple as wrapping it in cling wrap.
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"My dream is that one day you'll have two technicians with Ghostbusters backpacks come to your house and spray your roof," says Kramer, a post-doctoral fellow with The Edward S. Rogers Sr. Department of Electrical ...
This news release is available in German. The consumption of a sugary banquet before sex can have far-reaching consequences for a fruit fly and its offspring: it makes the young flies more prone to obesity. Together with researchers from Spain and Sweden, scientists from the Max Planck Institute of Immunobiology and Epigenetics in Freiburg have discovered that even a brief change in the diet of male fruit flies triggers obesity in the next generation. Specifically, high-sugar nutrition consumed one to two days before mating causes the male offspring to accumulate more ...
Computers are good at identifying patterns in huge data sets. Humans, by contrast, are good at inferring patterns from just a few examples.
In a paper appearing at the Neural Information Processing Society's conference next week, MIT researchers present a new system that bridges these two ways of processing information, so that humans and computers can collaborate to make better decisions.
The system learns to make judgments by crunching data but distills what it learns into simple examples. In experiments, human subjects using the system were more than 20 percent better ...
Study results that challenge the idea that bilingual speakers have a cognitive advantage are less likely to be published than those that support the bilingual-advantage theory, according to new research published in Psychological Science, a journal of the Association for Psychological Science. This research suggests that a publication bias in favor of positive results may skew the overall literature on bilingualism and cognitive function.
"Publishing only 'successful' studies means that we do not have access to many valuable studies that could increase our understanding ...
Toronto, Dec. 5, 2014 - The number of children and youth treated for concussions in both emergency departments and physician's offices in Ontario increased significantly between 2003 and 2010, with falls, hockey and skating injuries identified as the leading causes of pediatric concussion, according to a new joint study out of York University and the Institute for Clinical Evaluative Sciences (ICES).
The study," A population-based study of pediatric emergency department and office visits for concussions from 2003 to 2010", published today in the journal Paediatrics & ...
With so much focus on risk factors for disease, we are living in an era of surveillance medicine, in which the emphasis on risk blurs the lines between health and illness, argue researchers at Yale and Syracuse universities in a study published in the December issue of the Journal of Health and Social Behavior.
Co-authors Rene Almeling, assistant professor of sociology at Yale, and Shana Kushner Gadarian, assistant professor of political science at Syracuse University, conducted a nationwide survey of American adults to determine if healthy people react to hypothetical ...
The Ku Klux Klan's failure to defeat the black civil rights moment is well documented, but the group's lesser-known legacy may be its lasting impact on the U.S. political system, according to a paper published in the December issue of the American Sociological Review.
David Cunningham, professor and chair of the Department of Sociology at Brandeis University, Rory McVeigh of the University of Notre Dame and Justin Farrell of Yale University report that KKK activity played a significant role in shifting voters' political party allegiance in the South in the 1960s -- from ...
(NEW YORK - December 5, 2014) A key protein may represent a new way to use the immune system to speed healing and counter inflammatory, infectious and autoimmune diseases, according to study led by researchers at the Icahn School of Medicine at Mount Sinai and published in the December issue of Cell Reports.
The current study results revolve around proteinases, enzymes that break down proteins as part of cellular life. Matrix metalloproteinases or MMPs specifically target the extracellular matrix, the non-cell, structural framework within tissues. Beyond that role, ...
