Featured Research

from universities, journals, and other organizations

Crossover sound: Unambiguous evidence for coherent phonons in superlattices

Date:
February 5, 2014
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
The first "unambiguous demonstration" of the atomic-scale sound waves known as phonons crossing over from particle-like to wave-like behavior in superlattices opens the door to improved thermoelectrics and possibly even phonon lasers.

Electron microscopy-spectroscopy images of a strontium titanate/barium titanate superlattice film reveal the presence of atomically sharp interfaces with minimal intermixing. Superlattice is color-coded with strontium (orange) barium (purple) and titanium (green).
Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory

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."


Story Source:

The above story is based on materials provided by DOE/Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jayakanth Ravichandran, Ajay K. Yadav, Ramez Cheaito, Pim B. Rossen, Arsen Soukiassian, S. J. Suresha, John C. Duda, Brian M. Foley, Che-Hui Lee, Ye Zhu, Arthur W. Lichtenberger, Joel E. Moore, David A. Muller, Darrell G. Schlom, Patrick E. Hopkins, Arun Majumdar, Ramamoorthy Ramesh, Mark A. Zurbuchen. Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices. Nature Materials, 2013; 13 (2): 168 DOI: 10.1038/nmat3826

Cite This Page:

DOE/Lawrence Berkeley National Laboratory. "Crossover sound: Unambiguous evidence for coherent phonons in superlattices." ScienceDaily. ScienceDaily, 5 February 2014. <www.sciencedaily.com/releases/2014/02/140205143756.htm>.
DOE/Lawrence Berkeley National Laboratory. (2014, February 5). Crossover sound: Unambiguous evidence for coherent phonons in superlattices. ScienceDaily. Retrieved September 23, 2014 from www.sciencedaily.com/releases/2014/02/140205143756.htm
DOE/Lawrence Berkeley National Laboratory. "Crossover sound: Unambiguous evidence for coherent phonons in superlattices." ScienceDaily. www.sciencedaily.com/releases/2014/02/140205143756.htm (accessed September 23, 2014).

Share This



More Matter & Energy News

Tuesday, September 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Will Living Glue Be A Thing?

Will Living Glue Be A Thing?

Newsy (Sep. 23, 2014) Using proteins derived from mussels, engineers at MIT have made a supersticky underwater adhesive. They're now looking to make "living glue." Video provided by Newsy
Powered by NewsLook.com
Company Copies Keys From Photos

Company Copies Keys From Photos

Newsy (Sep. 22, 2014) A new company allows customers to make copies of keys by simply uploading a couple of photos. But could it also be great for thieves? Video provided by Newsy
Powered by NewsLook.com
The Hyped-Up Big Bang Discovery Has A Dust Problem

The Hyped-Up Big Bang Discovery Has A Dust Problem

Newsy (Sep. 22, 2014) An analysis of new satellite data casts serious doubt on a previous study about the Big Bang that was once hailed as revolutionary. Video provided by Newsy
Powered by NewsLook.com
Rockefeller Oil Heirs Switching To Clean Energy

Rockefeller Oil Heirs Switching To Clean Energy

Newsy (Sep. 22, 2014) The Rockefellers — heirs to an oil fortune that made the family name a symbol of American wealth — are switching from fossil fuels to clean energy. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins