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 VOL. 23, NO. 22APRIL 24, 1998 


Two Lucent Scientists Join Columbia, Will Research Condensed Matter

Horst Stormer and Aron Pinczuk. Record Photo by Eileen Barroso.


 BY BOB NELSON

At temperatures that approach absolute zero and in strong magnetic fields, electrons start to behave very strangely. As carriers of electric current, they appear to possess only a fraction of their normal charge. They can be made to travel as waves in quantum wires, and can be bound into new, artificial atoms called quantum dots. They can even enter superfluid states where they seem to move without friction or resistance.

  Two new tenured faculty at Columbia, Aron Pinczuk and Horst Stormer, are exploring these and other behaviors as they research the fundamental properties of semiconductors. The pair have conducted their research at Bell Labs, the research and development arm of Lucent Technologies Corp., and will remain affiliated with the laboratory.

  Pinczuk is known as a leading experimentalist of inelastic light scattering in semiconductors and Stormer as a co-discoverer of the fractional quantum Hall effect. Each accepted a joint appointment in the department of physics and the department of applied physics effective Jan. 1, and will be known as “professor of applied physics and physics.”

  Both work in the field of condensed matter physics, the study of condensed phases of matter such as solids and liquids. The field has grown into the largest specialty within physics, with tremendous intellectual and technological importance. The two new faculty members add important new strength to Columbia’s program in condensed matter physics and material science and will begin teaching advanced physics topics in the fall 1998 semester at both the graduate and undergraduate levels.

  It is the unique properties of semiconductors, the materials from which transistors are made, that lie at the heart of the computer revolution. Millions of interconnected transistors, each switching on and off hundreds of millions of times per second, provide the semiconductor “brain” controlling desktop personal computers as well as the fastest supercomputers. At present, semiconductors are used to switch electric currents, but a new generation of optoelectronic materials is being developed that can switch light instead of electricity, offering even higher levels of speed and miniaturization.

  The two physicists are investigating the fundamental properties of modern semiconductor structures, research that may eventually help create improved electronic devices such as computer chips or optoelectronic devices such as solid-state lasers. Their research focuses on structures at the scale of nanometers, or billionths of a meter, that are only a few hundred atoms across.

  “We are extremely pleased to have, in Aron Pinczuk and Horst Stormer, two brilliant new lights to add to the physics and applied physics departments at Columbia,” said Zvi Galil, dean of the Fu Foundation School of Engineering and Applied Science at Columbia.

  Pinczuk and Stormer study systems in which the current-carrying electrons do not move in all three spatial dimensions throughout the material but are confined to an extremely thin two-dimensional layer or one-dimensional line only a few hundred atoms thick. Electrons can be so confined by building up the semiconductor material in layers in such a way that one layer is different from the rest. This special layer provides a small attraction to the electrons as they move through the material. As the temperature is lowered, moving electrons have less energy and tend to occupy only quantum states located very near the special layer, finally abandoning all other quantum states at temperatures near absolute zero.

  Electrons forced to move in such confined structures display new, unexpected behavior, especially if a very intense magnetic field is applied. For example, such confined electrons display a new sort of electrical resistance that is precisely quantized into steps. This strange behavior implies that the fundamental current carriers are no longer individual electrons but instead electrons that as a group carry precisely a third to a fifth of the normal electronic charge. Stormer and colleagues were the first to observe this effect, called the fractional quantum Hall effect.

  Stormer observed the fractional quantum Hall effect by electrical transport—simply measuring the flow of electrical current—while Pinczuk used a different method, in elastic light scattering experiments.

  Pinczuk developed light scattering methods to study low-dimensional electron systems. Such experiments have uncovered new behaviors that emerge when electrons condense into exotic liquids.






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