Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

An exciting new state for excitons

26.08.2002


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 www.lbl.gov/.

For more information contact Leonid Butov at (510)486-7475
or via e-mail at LVButov@lbl.gov

Lynn Yarris | EurekAlert!

More articles from Physics and Astronomy:

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

nachricht Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
16.07.2018 | Chinese Academy of Sciences Headquarters

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: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

16.07.2018 | Life Sciences

New research calculates capacity of North American forests to sequester carbon

16.07.2018 | Earth Sciences

Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication

16.07.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>