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 Astronomers release most complete ultraviolet-light survey of nearby galaxies
18.05.2018 | NASA/Goddard Space Flight Center

nachricht A quantum entanglement between two physically separated ultra-cold atomic clouds
17.05.2018 | University of the Basque Country

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: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

Im Focus: Computer-Designed Customized Regenerative Heart Valves

Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.

Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...

Im Focus: Light-induced superconductivity under high pressure

A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.

Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Supersonic waves may help electronics beat the heat

18.05.2018 | Power and Electrical Engineering

Keeping a Close Eye on Ice Loss

18.05.2018 | Information Technology

CrowdWater: An App for Flood Research

18.05.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>