Subscribe free to our newsletters via your
. 24/7 Space News .




TECH SPACE
Shaking the topological cocktail of success
by Staff Writers
Zurich, Switzerland (SPX) Nov 13, 2014


A Mobius strip can't be transformed into a normal strip without cutting. Image courtesy Gregor Jotzu and ETH Zurich.

Graphene is the miracle material of the future. Consisting of a single layer of carbon atoms arranged in a honeycomb lattice, the material is extremely stable, flexible, highly conductive and of particular interest for electronic applications. ETH Professor Tilman Esslinger and his group at the Institute for Quantum Electronics investigate artificial graphene; its honeycomb structure consists not of atoms, but rather of light.

The researchers align multiple laser beams in such a way that they create standing waves with a hexagonal pattern. This optical lattice is then superimposed on potassium atoms in a vacuum chamber, which are cooled to near absolute zero temperature. Trapped in the hexagonal structure, the potassium atoms behave like the electrons in graphene.

"We work with atoms in laser beams because it provides us with a system that can be controlled better and observed more easily than the material itself," explains Gregor Jotzu, a doctoral student in Physics. Since the researchers focus primarily on understanding quantum mechanical interactions, they describe their system as a quantum simulator.

Thanks to this testing set-up, it has now become possible to implement an idea first published by the British physicist Duncan Haldane in 1988. Solid-state physicists had hoped they would be able to create the Haldane model with real graphene - in vain until now, says Esslinger: "Now we've done it with a different system. This is a beautiful and significant new step."

Breaking time-reversal symmetry
Haldane had suggested that it might be possible to create an entirely new class of materials with exceptional properties determined by their topology. Mathematically, objects have the same topology if they can be transformed into each other by continuous deformations, such as compression or stretching. For instance, an orange could be deformed into a banana.

If the transformation requires a cut, then two objects are topologically distinct; for example, a Mobius strip can not be transformed into a normal strip without first cutting and then reassembling it.

In the Haldane model, the system no longer has the same topology as ordinary materials. Implementing this system requires a special 'ingredient' and physicists speak about breaking a symmetry: time-reversal symmetry is broken. This means that the system does not behave in the same manner when time runs backwards.

Normally, a physical system appears the same whether time moves forward or backwards; that is, this symmetry-breaking does not occur. Theoretically, this could be realised in real materials using magnetic fields. However, the magnets would have to be smaller and placed more precisely than the distance between atoms in a solid - less than about 0.1 nanometres.

"The particles experience a twisted world"
Using the quantum simulator, the researchers can break time-reversal symmetry with a relatively simple trick, as they have just reported in the journal Nature. "We shake the entire system in a circular motion," says Jotzu.

The researchers placed small piezoelectric crystals on mirrors which reflect the laser light and then allowed them to vibrate. "It's even audible, roughly like a high flute tone," says the physicist. At the right frequency and amplitude, the atoms do not fall out of the laser lattice, as one might expect, but instead remain trapped.

When the researchers moved the system back and forth in a straight line, the atoms still behaved normally. But when shaken in a circular motion, "the particles experience a twisted world", explains Esslinger, just as the movement on a Mobius strip would differ from that on a normal one. The topology and hence the properties of the system changed as though it had become a completely different and new material.

Testing what does not yet exist
It was a surprise that they could implement the topological Haldane model experimentally, says the ETH professor; the experiment was "like shooting from the hip". The researchers celebrated their success fittingly with the right drink - shaken, not stirred. But Esslinger warns against drawing hasty conclusions: "We don't create new materials. We just tested a concept."

In this context, experiments with lasers and ultracold atoms can be superior to computer simulations when a system is too complex for calculations. "This allows us to investigate the properties of materials that don't even exist yet," says Jotzu.

It is still uncertain if the results obtained with the quantum simulator could one day be transferred to real materials. But there are already ideas: If circularly-polarised light could be sent on to real graphene, it may have a similar effect as shaking artificial graphene in a circular motion.

This was proposed by two visiting Japanese colleagues, says Esslinger. So it may be possible, for example, to make an insulator out of a conductive material using light - and vice versa. The electronic applications of such a system, which could react extremely fast, would be manifold.

Jotzu G, Messer M, Desbuquois R, Lebrat M, Uehlinger T, Greif D, Esslinger T. Experimental realization of the topological Haldane model with ultracold fermions. 2014. Nature, published online 13 November. DOI: 10.1038/nature13915


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only


.


Related Links
ETH Zurich
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








TECH SPACE
Drexel Engineers Improve Strength, Flexibility of Atom-Thick Films
Philadelphia PA (SPX) Nov 12, 2014
Making a paper airplane in school used to mean trouble. Today it signals a promising discovery in materials science research that could help next-generation technology -like wearable energy storage devices- get off the ground. Researchers at Drexel University and Dalian University of Technology in China have chemically engineered a new, electrically conductive nanomaterial that is flexible enoug ... read more


TECH SPACE
After Mars, India space chief aims for the moon

China examines the three stages of lunar test run

China gears up for lunar mission after round-trip success

NASA's LRO Spacecraft Captures Images of LADEE's Impact Crater

TECH SPACE
Warmth and flowing water on early Mars were episodic

Next NASA Mars Mission Reaches Milestone

Mars, too, has macroweather

Comet lander 'working well', but may be on slope

TECH SPACE
Tencent looks to the final travel frontier

ESA Commissions Airbus As contractor For Orion Service Module

Study Investigates How Men and Women Adapt Differently to Spaceflight

S3 concludes first phase of drop-tests

TECH SPACE
China publishes Earth, Moon photos taken by lunar orbiter

China plans to launch about 120 applied satellites

Mars probe to debut at upcoming air show

China to build global quantum communication network in 2030

TECH SPACE
Europe's 3D printer set for ISS

NASA Commercial Crew Partners Continue System Advancements

Astronaut turned Twitter star, Reid Wiseman, back on Earth

Three-man multinational space crew returns to Earth

TECH SPACE
Time-lapse video shows Orion's move to Cape Canaveral launch pad

Soyuz Installed at Baikonur, Expected to Launch Wednesday

SpaceX chief Musk confirms Internet satellite plan

Orbital recommits to NASA Commercial program and Antares

TECH SPACE
Follow the Dust to Find Planets

NASA's TESS mission cleared for next development phase

ADS primes ESA's CHEOPS to detect and classify exoplanets

NASA's TESS Mission Cleared for Next Development Phase

TECH SPACE
Shaking the topological cocktail of success

Drexel Engineers Improve Strength, Flexibility of Atom-Thick Films

Creating Bright X-Ray Pulses in the Laser Lab

New Process Isolates Promising Material




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news 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 Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.