Bardeen, John (physicist)

(1908-1991) American Theoretical Physicist, Solid State Physicist, Electrical Engineer

John Bardeen was a giant of solid state physics, whose greatest achievements were the invention of the transistor, with william bradford shockley and Walter Battrain, and the development of a comprehensive theory of superconductivity, with john robert schrieffer and Leon Cooper. These contributions made him the first person to win two Nobel Prizes in physics, in 1956 and 1972.

He was born on May 23, 1908, in Madison, Wisconsin, the second of five children born to Charles Russell Bardeen and Althea Harmer. His father was the first graduate of the Johns Hopkins Medical School and founder of the Medical School of the University of Wisconsin; his mother had studied art at the Pratt Institute in Brooklyn, New York, and practiced interior design in Chicago. John attended elementary and secondary schools in Madison. His brilliance was immediately apparent, and he was skipped from third grade to junior high. The death of his mother of cancer when he was 12 was a devastating blow. He managed to continue his studies, however, and entered the University of Wisconsin at age 15. He chose to major in engineering, both because of his love of mathematics and because he had no desire to be an academic as his father was.

He received a B.S. in electrical engineering in 1928 and an M.S. the following year, at the University of Wisconsin. Between 1928 and 1930, he was a graduate assistant, examining mathematical problems of antennas and working on applied geophysics. The Great Depression had begun and jobs were scarce. He managed to get hired by Gulf Research in Pittsburgh, where he worked on mathematical modeling of magnetic and gravitational oil prospecting surveys. This was an exciting period when geophysical methods were first being applied to oil prospecting. But Bardeen, who kept abreast of advances in physics, was increasingly drawn to pure science. In 1933, he gave up his industrial career and enrolled for graduate work at Princeton University with eugene paul wigner. At Princeton he was introduced to the rapidly developing field of solid state physics. Bardeen was fascinated by the work of such physicists as Wigner and Frederick Seitz, who were using the new quantum mechanics to help understand how semiconductors worked. He finished his dissertation on the theory of the work function of metals in 1935.

From 1935 to 1938 he was a junior fellow at Harvard University, where he worked with john housbrook van vleck and percy williams bridgman. In 1938, he married Jane Maxwell, a biologist who taught at a girls’ high school near Boston. It was to be an enduring union that would produce three children and six grandchildren. From 1938 to 1941, he was an assistant professor at the University of Minnesota. During World War II, between 1941 and 1945, he returned to applied physics at the Naval Ordnance Laboratory in Washington, D.C., where he investigated ways to protect U.S. ships and submarines from magnetic mines and torpedoes. In 1945 he joined the newly formed research group in solid state physics, which included Walter Brittain and was directed by William Shock-ley, at the Bell Telephone Laboratories in

John Bardeen invented the transistor and developed a comprehensive theory of superconductivity.

John Bardeen invented the transistor and developed a comprehensive theory of superconductivity.

Murray Hill, New Jersey, where his research on semiconductors led in 1947 to the development of the transistor. Physicists first understood the electrical properties of semiconductors in the late 1930s, when they became aware of the role of low concentrations of impurities in controlling the number of mobile charge carriers in materials. Current rectification (i.e., the conversion of oscillating current into direct current) at metal-semiconductor junctions had long been known, but the next step required was to produce amplification analogous to that achieved by vacuum tube technology. Shockley’s group began a program to control the number of charge carriers at semiconductor surfaces by varying the electric field.

Bardeen and Brittain worked together harmoniously, as Brittain designed the experiments and Bardeen worked out theoretical explanations for the results. In the spring of 1947, Shockley asked them to investigate the reason for the failure of an amplifier he had designed, which was based on a crystal of silicon, later replaced by germanium. By observing Brittain’s experiments, Bardeen realized that the assumption they had been making—that electrical current traveled through all parts of the germanium in the same way—was incorrect. On the contrary, electrons behave differently at the surface of the metal. If they could control what was happening at the surface, the amplifier should work. They demonstrated the effects of amplification of two metal contacts 0.05 mm apart on a germanium surface. Large variations of the power output through one contact were observed in response to tiny changes in the current through the other. On December 23, 1947, they succeeded in building the first point-contact transistor, the forerunner of the many complex devices now available through silicon chip technology. Bardeen, Brittain, and Shockley were awarded the Nobel Prize for this work in 1956.

In 1951, Bardeen left Bell and moved to the University of Illinois, where, with the graduate student Bob Schrieffer and postdoctoral student Leon Cooper, he developed the microscopic theory of superconductivity, known as the Bardeen-Cooper-Schrieffer (BCS) theory. In 1911, heike kammerlingh onnes had first observed zero electrical resistance in some metals below a critical temperature. Since then physicists had looked for a microscopic interpretation of this phenomenon of superconductivity. The methods that were successful in explaining the electric properties of normal metals were unable to predict the effect. At very low temperatures, metals were still expected to have a finite resistance due to scattering of mobile electrons by the ions in the crystal lattice. Bardeen’s solution to this problem was to show that electrons pair up through an attractive interaction, and that zero resistivity occurs when the thermal energy available is insufficient to break the pair apart.

Thus, for electrons embedded in a crystal, the normal Coulomb repulsion can be compensated for by this pairing effect when the temperature is below the critical value. The ion cores in the crystal lattice respond to the presence of a nearby electron, and the motion may result in the attraction of another electron to the ion. The net effect is an attraction between two electrons through the response of the ions in the solid. The BCS theory was based on the idea that the interaction between the electrons and the lattice leads to the formation of bound pairs of electrons, called Cooper pairs. The different pairs are strongly coupled to each other; this leads to a complex collective pattern in which a considerable fraction of the total number of conduction electrons are coupled to form a superconducting state. Because of the characteristic coupling of all the electrons, one cannot break up a single pair of electrons without also perturbing all the others, and this process requires an amount of energy that must exceed a critical value. Many of the remarkable qualities of superconductors can be understood qualitatively from the structure of this correlated many-electron state.

The comprehensive BCS theory has the ability to explain all known properties associated with superconductivity. Although applications of superconductivity to magnets and motors were possible without the BCS theory, the theory is important for strategies to increase the critical temperature as much as possible, since, if it could be raised above liquid nitrogen temperature, the economics of superconductivity would be transformed. In addition, the theory was an essential prerequisite for the prediction of Josephson junction tunneling, which has important applications in magnetometers and computers and in determination of the fundamental constants of physics. The BCS theory has had profound effects on nearly every field of physics from elementary particle to nuclear physics and from helium liquids to neutron stars. Bardeen and his two colleagues shared the Nobel Prize in physics for their theory in 1972.

During this period of intense theoretical work, he continued to be actively interested in engineering and technology. In 1951 he became a consultant for the Xerox Corporation (called Haloid at the time), and he continued work with them throughout their development as a technological giant. From 1961 to 1974, he was a member of the Board of Directors of the Xerox Corporation. He also was a consultant for General Electric Corporation for many years and for other technology firms.

In 1975 he became professor emeritus at Illinois, where he began working on theories for liquid helium 3 that have analogies with the BCS theory. He lived out the rest of his life in Urbana, Illinois, teaching, researching, and playing his favorite game, golf. He died in 1991 at the age of 82.

During his 60-year scientific career, Bardeen made important contributions to virtually every aspect of condensed matter physics, from his early work on the electronic behavior of metals, the surface properties of semiconductors, and the theory of diffusion of atoms in crystals to his later work on quasi-one-dimensional metals. In his 83d year he continued to publish original scientific papers. Both of Bardeen’s Nobel Prize-winning achievements have had a revolutionary impact on computer technology. The invention of the transistor led directly to the development of the integrated circuit and then the microchip.

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