Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


An exciting new state for excitons


A Bose-Einstein condensate, a form of matter heretofore only observed in atoms chilled to less than a millionth of a degree above absolute zero, may now have been observed at temperatures in excess of one degree Kelvin in excitons, the bound pairs of electrons and holes that enable semiconductors to function as electronic devices.

Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with a scientist at the University of California’s Santa Barbara campus, have reported the observation of excitons that display a macroscopically ordered electronic state which indicates they have formed a new exciton condensate. The observation also holds potential for ultrafast digital logic elements and quantum computing devices.

"The excitons were expected to form a quantum liquid or even a Bose-Einstein condensate, this state had been predicted in theory since the 1960s, but the macroscopically ordered exciton state that we found is a new state that was not predicted," says Leonid Butov, a solid state physicist who holds a joint appointment with Berkeley Lab’s Materials Sciences Division (MSD) and with the Institute of Solid State Physics at the Russian Academy of Sciences.

Just as the Nobel prize-winning creation of Bose-Einstein condensate atoms offered scientists a new look into the hidden world of quantum mechanics, so, too, would the creation of Bose-Einstein condensate excitons provide scientists with new possibilities for observing and manipulating quantum properties.

The creation of a new exciton condensate was reported in the August 15, 2002 issue of the journal Nature, in a paper co-authored by Butov, Arthur Gossard of UC Santa Barbara’s Department of Electrical and Computer Engineering, and Daniel Chemla, director of Berkeley Lab’s Advanced Light Source.

The new exciton condensate was observed at Berkeley Lab using photoluminescence on samples composed of the semiconductors gallium arsenide and aluminum gallium arsenide. The semiconductor samples were of extremely high quality and were prepared by Gossard in Santa Barbara.

The observations were made by shining laser light on specially designed nano-sized structures called quantum wells which were grown at the interface between the two semiconductors. These quantum wells allow electrons and electron holes (vacant energy spaces that are positively-charged) to move freely through the two dimensions parallel to the quantum well plane, but not through the perpendicular dimension. Under the right energy conditions, application of an electrical field in this perpendicular direction will bind an electron in one quantum well to a hole in another across a potential barrier to create a relatively stable exciton.

"An exciton functions as a quasi-particle, akin to a hydrogen atom," says Butov, "which means that by reducing temperature or increasing density, it is a candidate to form a Bose-Einstein condensate."

Trapped in the quantum wells, their movement restricted to two-dimensions, the excitons created by Butov and his colleagues condensed at the bottom of the wells as their temperature dropped. Because the mass of these excitons was so much smaller than that of the atoms used to form atomic Bose-Einstein condensates, the critical temperature at which condensation occurred, about one degree Kelvin (-272 degrees Celsius or -459 degrees Fahrenheit) was much higher. By comparison, to create the first atomic Bose-Einstein condensates back in 1995, researchers at the University of Colorado had the daunting task of chilling a ball of rubidium atoms to as close to absolute zero as the laws of physics allow.

Under photoluminescence, the macroscopically ordered exciton state that Butov and his colleagues observed appeared against a black background as a bright ring that had been fragmented into a chain of circular spots extending out to one millimeter in circumference.

"The existence of this periodic ordering shows that the exciton state formed in the ring has a coherence on a macroscopic length of scale," says Butov. "This coherence is a signature of a condensate. The next step is to do a coherence spectroscopy study, particularly at lower temperatures, that will verify the properties of this new state."

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our Website at

For more information contact Leonid Butov at (510)486-7475
or via e-mail at

Lynn Yarris | EurekAlert!

More articles from Physics and Astronomy:

nachricht 'Frequency combs' ID chemicals within the mid-infrared spectral region
16.03.2018 | American Institute of Physics

nachricht Fraunhofer HHI have developed a novel single-polarization Kramers-Kronig receiver scheme
16.03.2018 | Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, HHI

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: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>