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How to control friction in topologicalinsulators
BY BIOENGINEER — October 14, 2019 in Chemistry " 0
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Credit: Image: University of Basel, Departement of Physics
Topological insulators are innovative materials that conduct electricity on the surface, but act as insulators onthe inside. Physicists at the University of Basel and the Istanbul Technical University have begun investigating
how they react to friction. Their experiment shows that the heat generated through friction is significantly lowerthan in conventional materials. This is due to a new quantum mechanism, the researchers report in the scientificjournal Nature Materials.
Thanks to their unique electrical properties, topological insulators promise many innovations in the electronicsand computer industries, as well as in the development of quantum computers. The thin surface layer canconduct electricity almost without resistance, resulting in less heat than traditional materials. This makes themof particular interest for electronic components.
Furthermore, in topological insulators, the electronic friction – i.e. the electron-mediated conversion of electricalenergy into heat – can be reduced and controlled. Researchers of the University of Basel, the Swiss NanoscienceInstitute (SNI) and the Istanbul Technical University have now been able to experimentally verify anddemonstrate exactly how the transition from energy to heat through friction behaves – a process known asdissipation.
Measuring friction with a pendulum
The team headed by Professor Ernst Meyer at the Department of Physics of the University of Basel investigatedthe effects of friction on the surface of a bismuth telluride topological insulator. The scientists used an atomicforce microscope in pendulum mode. Here, the conductive microscope tip made of gold oscillates back and forthjust above the two-dimensional surface of the topological insulator. When a voltage is applied to the microscopetip, the movement of the pendulum induces a small electrical current on the surface.
In conventional materials, some of this electrical energy is converted into heat through friction. The result on theconductive surface of the topological insulator looks very different: the loss of energy through the conversion toheat is significantly reduced.
“Our measurements clearly show that at certain voltages there is virtually no heat generation caused byelectronic friction,” explains Dr. Dilek Yildiz, who carried out this work within the SNI PhD School.
A novel mechanism
The researchers were also able to observe for the first time a new quantum-mechanical dissipation mechanismthat occurs only at certain voltages. Under these conditions, the electrons migrate from the tip through anintermediate state into the material – similar to the tunneling effect in scanning tunneling microscopes. Byregulating the voltage, the scientists were able to influence the dissipation. “These measurements confirm thegreat potential of topological insulators, since electronic friction can be controlled in a targeted manner,” addsMeyer.
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Media ContactReto [email protected]
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http://dx.doi.org/10.1038/s41563-019-0492-3 .
Tags: Atomic/Molecular/Particle Physics Chemistry/Physics/Materials Sciences Electrical Engineering/Electronics
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Home ∠ NEWS ∠ Science News ∠ Biology
Researchers map the evolutionary history ofoaks
BY BIOENGINEER — October 14, 2019 in Biology " 0
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Credit: The Morton Arboretum
How oaks are related has long posed a challenge to scientists. Dr. Andrew Hipp, senior scientist at The MortonArboretum, led an international team of 24 scientists to unravel the history of global oak diversity for the firsttime using DNA sequencing of 260 oak species, combined with genomic mapping and fossil data.
Fundamental questions about relationships between organisms and the genes that drive ecologicaldiversification underlie the secrets of biodiversity. Understanding the past of this ecologically, economically andculturally important group provides a baseline of knowledge that will allow scientists to address additionalquestions about oaks and other trees, as well as help with conservation efforts.
“This paper demonstrates that oaks have repeatedly and globally diversified in response to ecologicalopportunity” says Hipp. “The changes in the global landscape have given us the gift of the oak diversity weobserve today.”
Patchwork of Histories
The new paper, to be published in New Phytologist, is available free through an Early View online for one monthbeginning October 14. The study provides the most detailed account to date of the evolutionary history of theworld’s oaks. Investigating which parts of the oak genome distinguish species from one another, researchers atThe Morton Arboretum, in collaboration with 17 institutions around the world, discovered that each gene orstretch of DNA in the genome has the potential to record multiple histories; each section bears the history ofspeciation of one oak lineage, but it may record the history of hybridization for a different lineage. In otherwords, there is no one region of the genome that defines oaks: it is the patchwork of histories embedded in thegenome that characterize the history of oak evolution.
In addition, this research shows that different oak lineages have repeatedly diversified in the same area. Redoaks, white oaks, ring-cupped oaks, turkey and cork oaks, and three of the other oak sections arose rapidly andsegregated to either the Americas or Eurasia. All of these lineages can be found in part of their range with atleast one other lineage. As oaks migrated, species interbred, hybridized and diversified opportunistically inresponse to changes in the landscape. The highest rates of species diversification have been in response tomigrations into new territory. Over and over, oaks have taken advantage of ecological opportunity to produce thediversity we see today, providing humans with ships, homes, wine barrels, furniture and acorns to eat, andproviding food and homes for countless insects, mammals, birds and fungi.
“For the first time, this paper demonstrates that the history of different [oak] lineages is driven by different setsof genes,” said co-author Dr. Antoine Kremer from the French National Institute for Agricultural Research. “Thestory of oak evolution is especially fascinating due to the ecological and morphological convergence in differentoak lineages that cohabit on the same continent.”
The importance of oaks
Oaks support the planet’s ecosystem like very few other tree species do. As both stately trees and dry-landshrubs, oaks are fundamental to the health of forests, providing critical food, habitat and shelter for animals,birds and insects, and have the highest amount of biomass compared to any other tree species in the forest,working harder to clean the air than many other tree species. Today, oaks need the help of people. Around theworld, oaks are under threat, due to pests, diseases and loss of habitat. If oaks are lost, it will upset the delicatebalance of forest ecosystems and leave humans without their benefits. Researchers and conservationists at The
Morton Arboretum are committed to ensuring oaks thrive. Learn more about what The Morton Arboretum isdoing to conserve oaks globally.
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About The Morton Arboretum
The Morton Arboretum is an internationally recognized outdoor tree museum and tree research center located inLisle, Illinois. As the champion of trees, the Arboretum is committed to scientifically-informed action, bothlocally and globally, and encouraging the planting and conservation of trees for a greener, healthier, and morebeautiful world. On 1,700 acres are 222,000 plant specimens representing 4,500 different kinds of plants, alongwith specialty gardens, educational exhibits, the award-winning Children’s Garden, 16 miles of hiking trails andthe Visitor Center, featuring The Arboretum Store and the Ginkgo Restaurant and Café. The Morton Arboretum is anot-for-profit 501(c)(3) charitable organization, welcoming 1.3 million visitors annually and serving 53,000member households in 2018. Learn more at mortonarb.org.
Media ContactTari [email protected]
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