Contact: Bob Nelson For immediate release
(212) 854-6580 April 15, 1998
New Columbia Faculty To Investigate
Fundamental Properties of Semiconductors
Pair Research Electrons' Unusual Behavior Under Extreme Conditions
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 University, 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.
Professor Pinczuk is known as a leading experimentalist of inelastic light
scattering in semiconductors and Professor 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 January
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.
By creating and studying systems of this size, these physicists are able to
develop new methods to unravel the mysteries of the quantum theory of electrons,
atoms and light. Structures this small are of immense technological importance
because they will be capable of faster switching speeds and can be used to
construct higher-density computer memories than is now possible.
"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. "Our research and teaching both rise a notch with
their arrival, as do our opportunities to collaborate in research projects with
William F. Brinkman, vice president physical sciences research at
Lucent's Bell Labs, said, "Bell Labs has a long tradition of collaborating with
universities on research and development. We hope the joint appointment will
help us establish a strong collaborative program with Columbia faculty and
students on the physics of semiconductors and related sciences."
Professors 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. Professor Stormer and colleagues Daniel Tsui at Princeton and Arthur
Gossard of the University of California, Santa Barbara, were the first to observe
this effect, called the fractional quantum Hall effect.
"Understanding these bizarre properties has been a major success of
condensed matter theory during the past decade," Professor Stormer said. "The
fractional quantum Hall effect is very important for our understanding of many-
particle physics, introducing as it does new ideas that may well have an
important future effect on other areas of science.
"While these new phenomena may not directly affect device technology, the
structures we use in these experiments are essentially the same as those being
used in high-performance current amplifiers."
For example, the same two-dimensional system in which Professor
Stormer has unraveled this counterintuitive behavior of electrons is the central
component of a metal-oxide semiconductor field-effect transistor, or MOSFET, in
which an input signal can control electrical current through the same two-
dimensional electron system, called a channel; the device is central to the
semiconductor industry. And the identical materials that are being used in
Professor Stormer's studies are also used to make high electron mobility
transistors, or HEMTs. Such transistors are used as highly-sensitive gatekeepers
in many of the new high-frequency, 2-gigahertz cellular phones.
More recently, both condensed matter physicists have turned to the
investigation of yet lower-dimensional systems, such as quantum wires embedded
in semiconductor materials, where electrons are free to move only back and forth
along a line. In such wires, electrons reveal their wave-like nature and travel
like light waves down a glass fiber. Physicists believe that by adding mirrors to
the ends of the wires, the quantum states of the electrons can be excited, creating
a new, very narrow-frequency type of laser. They are also studying quantum dots,
fully confined, zero-dimensional systems that act like artificial atoms.
Professor Stormer observed the fractional quantum Hall effect by electrical
transport - simply measuring the flow of electrical current - while Professor
Pinczuk used a different method, inelastic light scattering experiments.
Light scattering involves shining a light source, often a laser, on the
medium to be studied and then examining the light that scatters from it. Some
light reflects from the medium as from a mirror, but a small amount scatters in
many directions, much as the beams from a car's headlights scatter in the fog.
Details of the structure of a material can be learned by looking at the directions of
the scattering and whether there are any changes in the wavelength - or color -
of the light. When scientists examine elastic light scattering, they are looking at
light that scatters at the same wavelength as the reflected laser beam. When they
examine inelastic light scattering, they are looking at light that has its
wavelength shifted as a result of scattering.
"One can say that the energy of the photons, or quantized units of light, here
produced by a laser, that are reflected from the medium either gain or lose energy
from the medium," Professor Pinczuk said. The magnitude of this change in
photon energy - or, equivalently, the shift in the wavelength of the reflected light
- shows scientists critical details of the structure of the material, here
Professor Pinczuk developed light scattering methods to study low-
dimensional electron systems in low temperatures and intense magnetic fields.
Such experiments have uncovered new behaviors that emerge when electrons
condense into exotic liquids with unexpected properties, similar to those of
superfluids, such as supercooled helium, which flow with no apparent friction,
and superconductors, which conduct electricity with little or no electrical
resistance. His research has demonstrated that optical methods can contribute to
our understanding of these remarkable states of matter.
Both Professors Stormer and Pinczuk have won the American Physical
Society's prestigious Oliver E. Buckley Prize in Condensed Matter Physics,
Stormer in 1984 and Pinczuk in 1994.
Professor Pinczuk, who is from Buenos Aires, earned a Ph.D. in physics
from the University of Pennsylvania in 1969. After several research and teaching
positions in Buenos Aires, he took visiting scientist positions at the Max-Planck-
Institut in Stuttgart and then at IBM's Thomas J. Watson Research Center in
Yorktown Heights, N.Y., before joining the technical staff at AT&T Bell Labs. He
is a fellow of the American Physical Society and is the recipient of an honorary
doctorate from the Universidad Autonoma of Madrid.
Professor Stormer, a native of Frankfurt, earned a Ph.D. in physics from
the University of Stuttgart in 1977, having conducted his thesis research at the
Max-Planck-Institut's High Field Magnet Laboratory in Grenoble, France. He
joined AT&T Bell Laboratories in Murray Hill, N.J., in 1978 and was appointed
director of the Physical Research Laboratory there in 1992. He is a fellow of the
American Physical Society and of the American Academy of Arts and Sciences.
He will be awarded the Franklin Institute Medal in Physics with Dr. Tsui and
Robert Laughlin of Stanford on April 30 in Philadelphia.
Lucent Technologies, headquartered in Murray Hill, N.J., designs, builds
and delivers a wide range of public and private networks, communications
systems and software, data networking systems, business telephone systems and
microelectronics components. Bell Labs is the research and development arm of
the company. For more information on Lucent Technologies, visit the company's
web site at http://www.lucent.com.
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