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 Heating quantum matter: A novel view on topology
22.08.2017 | Université libre de Bruxelles

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell 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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Cholesterol-lowering drugs may fight infectious disease

22.08.2017 | Health and Medicine

Meter-sized single-crystal graphene growth becomes possible

22.08.2017 | Materials Sciences

Repairing damaged hearts with self-healing heart cells

22.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>