Princeton Weekly Bulletin October 19, 1998
Tsui wins Nobel Prize
Daniel
Tsui, Arthur Legrand Doty Professor of Electrical Engineering, has
won the 1998 Nobel Prize in Physics for his 1982 discovery with
co-winner Horst Störmer, now of Columbia University, of the
fractional quantum Hall effect. A third co-winner, Robert B.
Laughlin, explained their result the following year. The
experiments by Tsui and Störmer led to Laughlin's finding
that the electrons in a powerful magnetic field can form a quantum
fluid, in which "parts" of an electron can be identified.
Tsui's work stems from a 1879 finding by a student, Edwin Hall, who discovered a pattern in the flow of electric current when a gold plate is placed in a magnetic field at right angles to its surface. The current flowing along the plate would drop at right angles. This phenomenon, termed the Hall effect, can be used to determine the density of charge carriers in conductors and semiconductors and is a standard tool in physics laboratories.
In Hall's day, such experiments were performed at room temperature with moderate magnetic fields. By the 1970s, researchers could perform experiments at extremely low temperatures, with very powerful magnetic fields. The 1980 experiment by Klaus von Klitzing found that the Hall effect in the semiconductor silicon does not behave in a linear fashion, but instead creates "steps" along the strength of the magnetic field.
Tsui and Störmer, then at Bell Laboratories in Murray Hill, performed experiments on the quantum Hall effect in the semiconductor gallium arsenide, using even lower temperatures and more powerful magnetic fields. To do so, they created a unique environment, a trap in which to restrain electrons on a two-dimensional plane. This was done by sandwiching two dissimilar semiconductor wafers -- gallium arsenide on one side and gallium aluminum arsenide on the other. Electrons accumulated at the interface between the two semiconductors and were tightly confined. Next, the researchers cooled the electron trap down to a tenth of a degree above absolute zero.
To their surprise, Tsui and Störmer found that the next step in the Hall resistance was three times higher than von Klitzing's highest recorded step. Later, Tsui and Störmer found more steps, which initially could not be explained. The heights of the new steps could be expressed with the same constant used in earlier work, but were now divided by different fractions -- thus, the term fractional quantum Hall effect. This would be impossible, since electrons cannot have fractional charges. Laughlin later determined that the magnetic field had created "holes" in the two-dimensional sheet of electrons. Called vortices, these were similar to a whirlpool in a lake; in the absence of water, the vortices represent an absence of charge.
Born in Henan, China, Tsui came to the United States in 1958 to enter Augustana College, Rock Island, Ill., from which he graduated in 1961. He earned his PhD at the University of Chicago in 1967.
Tsui joined the Princeton faculty in 1982. He is the 29th winner of the Nobel Prize associated with Princeton University.
Photo: Denise Applewhite, April 1998