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 Interstellar seeds could create oases of life
28.08.2015 | Harvard-Smithsonian Center for Astrophysics

nachricht Draw out of the predicted interatomic force
28.08.2015 | Hiroshima University

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: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Interstellar seeds could create oases of life

28.08.2015 | Physics and Astronomy

An ounce of prevention: Research advances on 'scourge' of transplant wards

28.08.2015 | Health and Medicine

Fish Oil-Diet Benefits May be Mediated by Gut Microbes

28.08.2015 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>