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




TIME AND SPACE
Researchers Find Unambiguous Evidence for Coherent Phonons in Superlattices
by Lynn Yarris for Berkeley News
Berkeley CA (SPX) Feb 07, 2014


Surface topography of a 200 nanometer thick strontium titanate/ calcium titanate superlattice film on a strontium titanate substrate.

We all learn in high school science about the dual nature of light - that it exists as both waves and quantum particles called photons. It is this duality of light that enables the coherent transport of photons in lasers. Sound at the atomic-scale has the same dual nature, existing as both waves and quasi-particles known as phonons. Does this duality allow for phonon-based lasers?

Some theorists say yes, but the point has been argued for years. Recently a large collaboration, in which Berkeley Lab scientists played a prominent role, provided the first "unambiguous demonstration" of the coherent transport of phonons.

Ramamoorthy Ramesh, a senior scientist with Berkeley Lab's Materials Sciences Division, was a co-leader with Arun Majumdar, a former Associated Laboratory director at Berkeley Lab and currently VP for Energy at Google, of an experiment in which phonons underwent particle-to-wave crossovers in superlattices of perovskite oxides.

"Our observations open up new opportunities for studying the wave-like nature of phonons, particularly phonon interference effects," says Ramesh. "Such research should have potential applications in thermoelectrics and thermal management, and in the long run could help the development of phonon lasers."

Unlike elementary particles such as electrons and photons, whose wave nature and coherent properties are well-established, experimental demonstration of coherent wave-like properties of phonons has been limited.

This is because phonons are not true particles, but the collective vibrations of atoms in a crystal lattice that can be quantized as if they were particles. However, understanding the coherent wave nature of phonons is of fundamental importance to thermoelectrics, materials that can convert heat into electricity, or electricity into heat, which represent a potentially huge source of clean, green energy.

"Lower thermal conductivity is one of the keys to improving the efficiency of thermoelectric materials and the key to thermal conductivity in semiconductors is phonon transport," Majumdar says.

"Nanostructures such as superlattices are the ideal model systems for the study of phonon transport, particularly the wave-particle crossover, because the wavelength of the most relevant phonons are in the range of one to 10 nanometers."

Superlattices are artificial periodic structures consisting of two dissimilar semiconductors in alternating layers a few nanometers thick. For this demonstration, the collaboration synthesized high-quality superlattices of electrically insulating perovskite oxides on various single-crystal oxide substrates.

Interface densities in these superlattices were systematically varied using two different epitaxial growth techniques. Thermal conductivity was measured as a function of interface density.

"Our results were in general agreement with theoretical predictions of crossover from incoherent particle-like to coherent wave-like phonon transport," Ramesh says. "We also found sufficient evidence to eliminate extraneous or spurious effects, which could have alternatively explained the observed thermal conductivity minimum in these superlattices."

Capitalizing on the wave behavior of phonons should enable new advances in new heat transfer applications, the collaborators say. Furthermore, perovskite superlattice-based heterostructures could also serve as basic building blocks for the development of lasers in which beams of coherent phonons rather than coherent photons are emitted. Phonon lasers could provide advanced ultrasound imaging or highly accurate measuring devices, among other possibilities.

Ramesh is a corresponding author of a Nature Materials paper describing this research titled "Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices." For a complete list of the co-authors go here.

.


Related Links
Berkeley Lab
Understanding Time and Space






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








TIME AND SPACE
Quarks in the looking glass
Washington DC (SPX) Feb 06, 2014
From matching wings on butterflies to the repeating six-point pattern of snowflakes, symmetries echo through nature, even down to the smallest building blocks of matter. Since the discovery of quarks, the building blocks of protons and neutrons, physicists have been exploiting those symmetries to study quarks' intrinsic properties and to uncover what those properties can reveal about the physica ... read more


TIME AND SPACE
Astrobotic Begins Testing at Masten Space Systems

NASA bets on private companies to exploit moon's resources

NASA Extends Moon Exploring Satellite Mission

NASA's LRO Snaps a Picture of NASA's LADEE Spacecraft

TIME AND SPACE
Mars rover successfully negotiates risky move over sand dune

MAVEN on Track to Carry Out its Science Mission

NASA Mars Orbiter Examines Dramatic New Crater

Russia proposes water-hunting instrument for future Mars rover

TIME AND SPACE
NASA EDGE Showcases Three Technology Demonstration Missions

NASA Technology to Help Develop Noninvasive Medical Treatments

NASA Evolves Student Rocketry Challenge, Enhances Ties to Space Launch System

Report: U.S. science and technology lead diminishing as Asia competes

TIME AND SPACE
Moon plays trick on Jade Rabbit

Waiting for Yutu

'Goodnight, humans': Says Yutu As The Sun Sets

Extra Time for Tiangong

TIME AND SPACE
Andrews Space Cargo Module Power Unit Provides Power For Payloads Bound For ISS

Russian Progress M-22M docks with ISS following fast rendezvous

Russian Resupply Spacecraft Begins Expedited Flight to Station

NASA Selects Physical Science Research Proposals for the ISS

TIME AND SPACE
Ariane 5's heavy-lift mission is an on the numbers launch success

Antrix to launch UK and Singapore satellite using India's Polar Satellite Launcher

Russian Telecoms Satellites Readied for March Launch

58th successful launch in a row of Ariane 5

TIME AND SPACE
Kepler Finds a Very Wobbly Planet

One planet, two stars: new research shows how circumbinary planets form

First Weather Map of Brown Dwarf

NASA-Sponsored 'Disk Detective' Lets Public Search for New Planetary Nurseries

TIME AND SPACE
MDA announces Canada's DND Sapphire satellite completes commissioning

Scalable Agile Beam Radar Rapidly Achieves Major Program Milestones

NASA Boards the 3-D-Manufacturing Train

Amazon buys videogame studio Double Helix




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. 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 Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement