Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

UC San Diego Physicists Find Patterns in New State of Matter

30.03.2012
Physicists at the University of California, San Diego have discovered patterns which underlie the properties of a new state of matter.

In a paper published in the March 29 issue of the journal Nature, the scientists describe the emergence of “spontaneous coherence,” “spin textures” and “phase singularities” when excitons—the bound pairs of electrons and holes that determine the optical properties of semiconductors and enable them to function as novel optoelectronic devices—are cooled to near absolute zero.

This cooling leads to the spontaneous production of a new coherent state of matter which the physicists were finally able to measure in great detail in their basement laboratory at UC San Diego at a temperature of only one-tenth of a degree above absolute zero.

The discovery of the phenomena that underlie the formation of spontaneous coherence of excitons is certain to produce a better scientific understanding of this new state of matter. It will also add new insights into the quirky quantum properties of matter and, in time, lead to the development of novel computing devices and other commercial applications in the field of optoelectronics where understanding of basic properties of light and matter is needed.
The research team was headed by Leonid Butov, a professor of physics at UC San Diego who in 2002 discovered that excitons, when made sufficiently cold, tend to self-organize into an ordered array of microscopic droplets, like a miniature pearl necklace.

Using a state of the art refrigeration system, the UC San Diego physicists were able to achieve temperatures ten times colder than that earlier effort, enabling them with an instrument called an interferometer to measure coherence and spin of each pearl or bead within this necklace.

What they discovered was that the exciton particles’ spin is not homogenous in space, but forms patterns around these beads, which they call “spin textures.” They also discovered that a pattern of spontaneous coherence is correlated with a pattern of spin polarization and with phase singularities in the coherent exciton gas.

“It was a surprise to see this pattern,” said Alex High, a graduate student and the first author of the paper. “And it was even more surprising that polarization measurements showed that there was a strong correlation between the coherence and polarization.”

“We are working both on understanding the basic properties of excitons and on the development of excitonic signal processing,” said Butov. “The physics of excitons is interesting by itself. Furthermore, understanding the basic properties of excitons is needed to build excitonic devices in the future.”

The physicists created the excitons by shining a laser on cooled samples of gallium arsenide, the same semiconducting material used to make transistors in cell phones.

The light kicks electrons out of the atomic orbitals they normally occupy inside of the material. And this creates a negatively charged “free” electron and a positively charged “hole.”

The force of electric attraction keeps these two objects close together, like an electron and proton in a hydrogen atom. It also enables the exciton to exist as a single particle rather than a non-interacting electron and hole. However, since the electron and hole remain in close proximity, they sometimes annihilate one another in a flash of light, similar to annihilation of matter and antimatter.

To control this annihilation, Butov and his team separate electrons and their holes in different nano-sized structures called quantum wells. This allows creation of excitons with the required lifetime, about 50 nanoseconds in the experiment.

“During that time, they cool down, form condensates and demonstrate interesting spin physics,” said High. “Eventually the electron and hole recombine and the light comes back out.”

In their experiments, the physicists sent that emission through a complex set of mirrors called an interferometer, which divides the light into two different paths. This allowed them to compare two spatially separated regions of the same sample, enabling them to see the fine details of spontaneous coherence in excitons that had never been seen before.

“Previous experiments required fiber optics to do any sort of optical measurements in a dilution refrigerator,” said High. “But with this equipment, we can actually take pictures of the excitons at extremely low temperatures.’

“This is a very interesting discovery,” he added. “There’s very rich physics involved.”

Other members of the research team were UC San Diego graduate students Jason Leonard and Aaron Hammack; Michael Fogler, associate professor of physics at UC San Diego; Alexey Kavokin of the University of Southampton; and Arthur Gossard and Ken Campman of UC Santa Barbara’s materials science department. The research project was supported by grants from the US. Department of Energy, National Science Foundation and U.S. Army Research Office.
Media Contact
Kim McDonald, 858-534-7572, kmcdonald@ucsd.edu

Comment: Leonid Butov (858) 822-0362, lvbutov@ucsd.edu

Kim McDonald | EurekAlert!
Further information:
http://ucsdnews.ucsd.edu/pressreleases/uc_san_diego_physicists_find_patterns_in_new_state_of_matter/

More articles from Physics and Astronomy:

nachricht Telescopes team up to find distant Uranus-sized planet through microlensing
31.07.2015 | NASA/Goddard Space Flight Center

nachricht California 'rain debt' equal to average full year of precipitation
31.07.2015 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Quantum Matter Stuck in Unrest

Using ultracold atoms trapped in light crystals, scientists from the MPQ, LMU, and the Weizmann Institute observe a novel state of matter that never thermalizes.

What happens if one mixes cold and hot water? After some initial dynamics, one is left with lukewarm water—the system has thermalized to a new thermal...

Im Focus: On the crest of the wave: Electronics on a time scale shorter than a cycle of light

Physicists from Regensburg and Marburg, Germany have succeeded in taking a slow-motion movie of speeding electrons in a solid driven by a strong light wave. In the process, they have unraveled a novel quantum phenomenon, which will be reported in the forthcoming edition of Nature.

The advent of ever faster electronics featuring clock rates up to the multiple-gigahertz range has revolutionized our day-to-day life. Researchers and...

Im Focus: Superfast fluorescence sets new speed record

Plasmonic device has speed and efficiency to serve optical computers

Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.

Im Focus: Unlocking the rice immune system

Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight

A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...

Im Focus: Smarter window materials can control light and energy

Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.

By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

3rd Euro Bio-inspired - International Conference and Exhibition on Bio-inspired Materials

23.07.2015 | Event News

Clash of Realities – International Conference on the Art, Technology and Theory of Digital Games

10.07.2015 | Event News

World Conference on Regenerative Medicine in Leipzig: Last chance to submit abstracts until 2 July

25.06.2015 | Event News

 
Latest News

Tool making and additive technology exhibition: Fraunhofer IPT at Formnext

31.07.2015 | Trade Fair News

First Siemens-built Thameslink train arrives in London

31.07.2015 | Transportation and Logistics

California 'rain debt' equal to average full year of precipitation

31.07.2015 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>