Robert B. Laughlin
Laughlin, Robert B. (1950-), an American theoretical physicist, shared the 1998 Nobel Prize in physics with Horst Ludwig Störmer of Germany and Daniel Chee Tsui of the United States for their discovery of a new form of fluid called a quantum fluid. It was Laughlin, the theorist, who analyzed the results of their experiments and explained a baffling phenomenon called the fractional quantum Hall effect. In this phenomenon, it seemed that electrons—the particles making up electric currents—had been divided into parts. Laughlin showed that, in reality, the electrons coordinated their movements in a way that simulated the behavior of particles with fractional charges.
The original Hall effect had been discovered in 1879 by the American physicist Edwin H. Hall. When an electric current flows in an electrical conductor through which a magnetic field passes, the electrons (or other carriers of charge) feel a force from the magnetic field that makes them pile up on one side of the conductor. The piling up of electrons causes a sideways voltage across the wire, called the Hall voltage. The Hall voltage increases as the applied magnetic field is increased. The effect is of great practical importance because, among other things, it enables the number of charge carriers in a volume of the material to be measured.
A German physicist, Klaus von Klitzing, presented a paper in 1977 showing that at low temperatures, the Hall effect was quantized—that is to say, it changes in steps, rather than smoothly, as the field changed continuously. In 1981, Tsui and Stormer studied this quantum Hall effect at lower temperatures and stronger magnetic fields than von Klitzing had used. They found the Hall effect occurring in steps—but steps suggesting that it was being produced by electrons with fractional charges 1/3, 2/3, 2/5, 3/7, and so on. This phenomenon is called the fractional quantum Hall effect.
Within a year of the discovery, Laughlin had produced an explanation. The electrons had formed a new kind of quantum fluid. A quantum fluid is superconducting—that is, it has no electrical resistance—and superfluid—that is, it flows perfectly freely. Single electrons cannot form a quantum fluid, but if they can link up to move collectively, they can form “quasiparticles,” which comprise the superfluid. This linking of electrons is what happens in the fractional quantum Hall effect, and it is the quasiparticles that are fractionally charged.
Laughlin was born in Visalia, California. He earned his Ph.D. degree in physics at Massachusetts Institute of Technology (MIT) in 1979. He became a professor of physics at Stanford University in Palo Alto, California, in 1989.