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Research Update: Researchers observe “crowd behavior” in semiconductors

Using atomic-scale measurements, scientists at JILA (which originally stood for the Joint Institute for Laboratory Astrophysics but now encompasses a wider breadth of science)—a joint venture of NIST (National Institute of Standards and Technology, www.nist.gov) and the University of Colorado at Boulder—have revealed a previously unknown type of collective behavior among semiconductor particles. The effect could prove helpful in the development of optoelectronicdevices.

The researchers shot a sample of GaAs (gallium arsenide) with 100-fsec pulses of nearinfrared laser light. Analyzing how the semiconductor altered the intensity and phase of the light, the researchers teased out a subtle coupling between pairs of particles called “excitons.” By proving that excited particles oscillate in concert, the work supports advanced theoretical calculations about the electronic properties of semiconductors, thus refi ning scientists’ ability to predict the magnitude and phase of emissionsignals.

Meanwhile, in another research project spying on group activity among electrons, researchers at the Massachusetts Institute of Technology have developed a novel spectroscopy technique that measures energy levels with resolution 1000 times greater than othermethods.

The work applies to electrons confi ned within 2-D planes—an arrangement that fi nds use in laboratory work and in high-frequency amplifi ers, such as those in cell phones. The technique relies on quantum tunneling. By using short electrical pulses to induce electrons to tunnel from a 2-D system to a 3-D system and measuring the resulting voltage difference, the scientists deduced the energy state of the electrons in the 2-D system, accordingto MIT.

The experiments, which took place within a semiconducting crystal cooled to 0.1 above absolute zero, have revealed some surprising behavior, according to the researchers, who expect the technique to yield additional insights into physical phenomena involvingelectrons.

JILA, jilawww.colorado.edu.
Massachusetts Instituteof Technology, www.mit.edu.