Robert B. Laughlin

Robert B. Laughlin, born in 1950, American physicist and Nobel Prize winner. Laughlin shared the 1998 Noble Prize in physics with Chinese-born American physicist Daniel Tsui and German-born American physicist Horst Stormer. The three men collaborated on the discovery that electrons (tiny, negatively charged particles) can act together to form particle-like units called quasiparticles. When electrons form these quasiparticles, they appear to have only a fraction of their normal electric charge. Laughlin provided the theoretical analysis to explain Stormer and Tsui's experimental discovery of this phenomenon, called the fractional quantum Hall effect.

Laughlin was born in Visalia, California. He graduated with a bachelor’s degree in physics from the University of California at Berkeley in 1972. He continued his studies of physics at the Massachusetts Institute of Technology in Cambridge, Massachusetts, where he received his doctorate in physics in 1979.

In 1979 Laughlin went to work at AT&T’s Bell Laboratories, now part of Lucent Technologies, in New Jersey. In 1982 he became a research physicist at Lawrence Livermore National Laboratory in California. He became an associate professor of physics at Stanford University in California in 1985 and a professor of physics at Stanford in 1989.

Laughlin did the work for which he won the Nobel Prize at Bell Labs in the early 1980s. Stormer and Tsui also worked at Bells Labs at that time. Stormer and Tsui discovered that electrons in certain conditions behave very strangely, appearing to have only a fraction of the electrical charge of individual electrons.

The experiment Stormer and Tsui performed was based on the Hall effect, a phenomenon discovered in 1879 by American physicist Edwin Hall. The Hall effect occurs when scientists place a conductor (a material that allows electricity to flow through it easily) carrying an electric current in a magnetic field. A magnetic field is a region of space surrounding a magnet that exerts a force on electrically charged or magnetized objects. The magnetic field in the Hall effect pushes electrons in the conductor off to one side of the conductor, creating an electric charge difference from one side of the material to the other. The current flows through the conductor, but a charge difference, or voltage, occurs from one side of the conductor to the other. For example, if the conductor is in the shape of a long, narrow rectangle and the current flows from one short end to the other, the voltage will occur from one long end to the other.

Stormer and Tsui studied conductors at very low temperatures. The electric characteristics, including the Hall effect, of materials change at low temperatures. In 1980 German physicist Klaus-Olaf von Klitzing examined the behavior of conductors at temperatures near absolute zero (-273° C, or –459° F). Von Klitzing also used very strong magnetic fields. He discovered that, in those conditions, the voltage created by the Hall effect does not change smoothly but varies in discrete steps. Von Klitzing won the 1985 Nobel Prize in physics for this discovery, called the integer quantum Hall effect, or quantized Hall effect.

Quantum theory, an area of physics that describes both electrons and radiation in terms of both waves and particles, explains these steps. Quantum theory states that electrons in a magnetic field move in circular orbits perpendicular, or at right angles, to the magnetic field. These orbits are also called energy levels. The number of electrons that each orbit can hold depends on the strength of the magnetic field—the stronger the magnetic field, the more electrons can share a single energy level. As von Klitzing gradually increased the strength of the magnetic field, the electrons would begin to collect at one side of the conductor. When the first energy level was full, the voltage would level off, then drop suddenly as electrons started filling up another energy level. Each new energy level created a new step in voltage. Each step was made up of a whole number of electrons, so the voltage difference between steps was always greater than or equal to the charge of an electron.

In 1982 Stormer and Tsui were testing the integer quantum Hall effect, but at temperatures even lower and in magnetic fields even stronger than those used by von Klitzing. They expected to see steps of charge equal to the electrical charge of a whole electron, as von Klitzing had discovered. Instead, they found that the steps were more numerous and smaller than the integer quantum Hall effect predicts. Stormer and Tsui knew that they had made an important discovery, but they could not explain what had happened. Electrons cannot split into smaller particles, and they could find no reason that the steps would be fractions of the charge of an electron.

Laughlin saw Stormer and Tsui’s results and set out to explain them using quantum mechanical equations, the rules that describe the motion of subatomic particles (see Quantum Theory). In 1983 Laughlin developed a new theory that involved groups of electrons acting together as a unit. He called these units quasiparticles. Laughlin’s theory explains that each electron can belong to more than one quasiparticle and divide its charge between the quasiparticles. This allows for fractions of the charge of an electron to appear. In 1997 two groups of physicists saw direct evidence of quasiparticles. The effect, known as the fractional quantum Hall effect, does not have any immediate practical applications but may allow physicists to understand more about how the electrons in the early universe behaved. It also shows that the laws of quantum mechanics are powerful enough to explain new phenomena.

Laughlin continued his work in physics by studying high-temperature superconductivity when he moved to Stanford University in 1985. Superconductivity is a phenomenon that occurs in special materials below certain temperatures; electricity flows without resistance in these materials. Most superconductivity only occurs at very low temperatures. Laughlin’s work dealt with superconductivity that occurs at relatively high temperatures for superconductors, far above absolute zero. He also continued to develop mathematical models using the fractional quantum Hall effect.