Berkeley CA (SPX) Dec 21, 2010
Mobius symmetry, the topological phenomenon that yields a half-twisted strip with two surfaces but only one side, has been a source of fascination since its discovery in 1858 by German mathematician August Mobius. As artist M.C. Escher so vividly demonstrated in his "parade of ants," it is possible to traverse the "inside" and "outside" surfaces of a Mobius strip without crossing over an edge.
For years, scientists have been searching for an example of Mobius symmetry in natural materials without any success. Now a team of scientists has discovered Mobius symmetry in metamaterials - materials engineered from artificial "atoms" and "molecules" with electromagnetic properties that arise from their structure rather than their chemical composition.
Xiang Zhang, a scientist with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and a professor at the University of California (UC) Berkeley, led a study in which electromagnetic Mobius symmetry was successfully introduced into composite metamolecular systems made from metals and dielectrics. This discovery opens the door to finding and exploiting novel phenomena in metamaterials.
"We have experimentally observed a new topological symmetry in electromagnetic metamaterial systems that is equivalent to the structural symmetry of a Mobius strip, with the number of twists controlled by sign changes in the electromagnetic coupling between the meta-atoms," Zhang says.
"We have further demonstrated that metamaterials with different coupling signs exhibit resonance frequencies that depend on the number but not the locations of the twists. This confirms the topological nature of the symmetry."
Working with metallic resonant meta-atoms configured as coupled split-ring resonators, Zhang and members of his research group assembled three of these identical meta-atoms into trimers.
Through careful design of the electromagnetic couplings between the constituent meta-atoms, these trimers displayed Mobius C3 symmetry - meaning Mobius cyclic symmetry through three rotations of 120 degrees. The Mobius twists result from a change in the signs of the electromagnetic coupling constants between the constituent meta-atoms.
"The topological Mobius symmetry we found in our meta-molecule trimers is a new symmetry not found in naturally occurring materials or molecules." Zhang says.
"Since the coupling constants of metamolecules can be arbitrarily varied from positive to negative without any constraints, the number of Mobius twists we can introduce are unlimited. This means that topological structures that have thus far been limited to mathematical imagination can now be realized using metamolecules of different designs."
Details on this discovery have been published in the journal Physical Review Letters, in a paper titled "Optical Mobius Symmetry in Metamaterials." Co-authoring the paper with Zhang were Chih-Wei Chang, Ming Liu, Sunghyun Nam, Shuang Zhang, Yongmin Liu and Guy Bartal.
Xiang Zhang is a principal investigator with Berkeley Lab's Materials Sciences Division and the Ernest S. Kuh Endowed Chaired Professor at UC Berkeley, where he directs the Center for Scalable and Integrated NanoManufacturing (SINAM), a National Science Foundation Nano-scale Science and Engineering Center.
In science, symmetry is defined as a system feature or property that is preserved when the system undergoes a change. This is one of the most fundamental and crucial concepts in science, underpinning such physical phenomena as the conservation laws and selection rules that govern the transition of a system from one state to another.
Symmetry also dictates chemical reactions and drives a number of important scientific tools, including crystallography and spectroscopy.
While some symmetries, such as spatial geometries, are easily observed, others, such as optical symmetries, may be hidden. A powerful investigative tool for uncovering hidden symmetries is a general phenomenon known as "degeneracy."
For example, the energy level degeneracy of an atom in a crystal is correlated with the crystal symmetry. A three-body system, like a trimer, can be especially effective for studying the correlation between degeneracy and symmetry because, although it is a relatively simple system, it reveals a rich spectrum of phenomena.
"The unique properties of a three-body system make experimental investigations of hidden symmetries possible," says Chih-Wei Chang, a former post-doc in Zhang's group and the lead author of the paper in Physical Review Letters, says.
"Intrigued by the extraordinary engineering flexibilities of metamaterials, we decided to investigate some non-trivial symmetries hidden beneath these metamolecules by studying their degeneracy properties"
The authors tested their metamaterials for hidden symmetry by shining a light and monitoring the optical resonances. The resulting resonant frequencies revealed that degeneracy is kept even when the coupling constants between meta-atoms flip signs.
"Because degeneracy and symmetry are always correlated, there must be some symmetry hidden beneath the observed degeneracy" says Chang.
The researchers showed that whereas trimer systems with uniform negative (or positive) coupling signs could be symbolized as an equilateral triangle, trimer systems with mixed signs of couplings could only be symbolized as a Mobius strip with topological C3 symmetry. Furthermore, in other metamolecular systems made of six meta-atoms, the authors demonstrated up to three Mobius twists.
Says Chang, now a faculty member at National Taiwan University in Taipei, "When going from natural systems to artificial meta-atoms and metamolecules, we can expect to encounter phenomena far beyond our conventional conceptions. The new symmetries we find in metamaterials could be extended to other kinds of artificial systems, such as Josephson junctions, that will open new avenues for novel phenomena in quantum electronics and quantum optics."
Share This Article With Planet Earth
Lawrence Berkeley National Laboratory (Berkeley Lab)
Space Technology News - Applications and Research
Physicist Developing And Improving Designer optical Materials
Ames Io (SPX) Dec 20, 2010
Advancements in fabrication technologies may lead to superlenses and other designer optical materials, according to an Iowa State University and Ames Laboratory physicist. In an article titled "Improving Metamaterials" published in the Perspectives section of the journal Science, Costas Soukoulis and Martin Wegener write about the man-made materials designed to deliver certain properties n ... read more
Berkeley Researchers Discover Mobius Symmetry In Metamaterials|
German publisher Springer unveils iPad-only project
Japan telecom firm KDDI to start e-book distribution
New Google TV sets facing delays: reports
Arianespace Will Orbit Sicral 2 Milcomms Satellites
Codan Receives JITC Certification For 2110 HF Manpack
Northrop Grumman Bids for Marine Corps Common Aviation CnC
DSP Satellite System Celebrates 40 Years
ISRO Puts Off GSLV Launch
Arianespace To Launch ESA's First Sentinel Satellite
ISRO Set To Launch Heaviest Satellite For Telecom And TV
The Flight Of The Dragon
Universal Address And GPS Enhanced Google Maps For iPhones
New GeoGroups App Reinvents Geo-Social Experience
NAVTEQ Expands Global R And D Capabilities
Officials Complete GPS Software Upgrade Ahead Of Schedule
China opens skies to private air transport
European airports race to clear Christmas backlog
Air Force Flight Control Improvements
Britain's axed Harrier jets take final flight
S.Korea's Hynix says chip price slump will hit Q4 profit
Making Wafers Faster By Making Features Smaller
Taiwan scientists claim microchip 'breakthrough'
Plant Consumption Rising Significantly As Population And Economies Grow
NASA Satellite Data Addresses Needs Of California Growers
Satellites Give An Eagle Eye On Thunderstorms
Unstable Antarctica: What's Driving Ice Loss
Ecology watchdog warns of future damage from Hungary spill
New Catalysts Hold Promise For Air Quality
Toxic Toy Crisis Requires Fresh Solutions
Arrests in Greece over disputed waste landfill
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2010 - SpaceDaily. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement|