Leon Neil Cooper
Cooper, Leon Neil (1930-) is an American theoretical physicist who contributed to the development of the theory of superconductivity (the loss of all electrical resistance by some materials when cooled below a certain temperature).
Cooper shared the 1972 Nobel Prize in physics with his American colleagues John Bardeen and John Robert Schrieffer. Theoretical physicists make predictions based on the laws and theories of physics that they develop. These laws and theories are almost always expressed in the language of mathematics, a basic tool of physics. Experimental physicists perform carefully designed experiments and then compare their results to what was predicted to happen by theoretical physicists.
Leon Neil Cooper was born on Feb. 28, 1930, in New York City, to Irving Cooper and Anna Zola Cooper. After attending the Bronx High School of Science, Cooper entered Columbia University in New York City, where he majored in physics. There he earned his B.A. degree in 1951, his M.A. degree in 1953, and his Ph.D. degree in 1954. He specialized in quantum field theory, which describes the interaction of particles and fields at atomic or subatomic levels.
After serving a National Science Foundation fellowship at the Institute for Advanced Study, in Princeton, New Jersey, Cooper moved to the University of Illinois (UI) in Urbana in 1955, where he worked with Bardeen and Schrieffer. Bardeen became professor of electrical engineering and of physics at UI in 1951. Schrieffer was a graduate student who was studying under Bardeen. He worked out a problem dealing with electrical conduction on semiconductor surfaces, after which he spent a year in the laboratory, applying the theory to several surface problems. In his third year of graduate studies, he joined Bardeen and Cooper in developing the theory of superconductivity. This work would be Schrieffer's doctoral dissertation.
The work Cooper and his two colleagues did in the 1950's built on that of the Dutch physicist Heike Kamerlingh Onnes, who discovered superconductivity in 1911. Kamerlingh Onnes made the discovery while measuring the electrical resistance of frozen mercury. He found that when some metals are cooled to within a few degrees of absolute zero, they lose all resistance to the flow of electricity. This is the phenomenon known as superconductivity. Absolute zero is the theoretical temperature at which the atoms and molecules of a substance have the least possible energy. That temperature is -273.15°C (-459.67 °F). Lead and mercury become good superconductors near absolute zero. But some ceramics become superconductors at temperatures as high as -138 °C (-216 °F).
Bardeen proposed that superconductivity depends on the interaction of electrons with atomic vibrations. Bardeen and his colleagues studied these interactions for several years. Cooper joined them in 1956, making a major contribution to their theory that year with his discovery that electrons are attracted to each other in superconductors, materials that lose all resistance to the flow of current at low temperatures. Conductors are substances through which electric current flows easily. The number of free electrons in a substance determines how well it conducts current. Such metals as aluminum, copper, silver, and gold are good conductors because they have at least one free electron per atom. Some metals, such as lead and tin, are poorer conductors than other metals because they have less than one free electron per atom. Poor conductors resist the flow of electric current more than good conductors do.
In an ordinary electrical conductor, the atoms are arranged in a regular pattern called a lattice. Cooper made an important step in understanding superconductivity when he discovered that, at low temperatures, electrons (tiny particles carrying one unit of negative electric charge) could affect each other via the lattice. An electron moving through the lattice distorts it slightly, and the distorted lattice affects other electrons. Cooper found that this interaction could cause an electron, in effect, to attract another, so that the two electrons move together through the lattice. These electrons became known as Cooper pairs. Schrieffer made a further advance when he found that at low temperatures all the Cooper pairs in a conductor could move together. He built on Cooper's work when he discovered a method for analyzing the motions of large numbers of Cooper pairs.
Schrieffer, Bardeen, and Cooper soon extended Schrieffer's model into a general theory of superconductivity. This theory is usually called the BCS theory from the initials of the three scientists who worked on it—Bardeen, Cooper, and Schrieffer.
The BCS theory states that the interaction between Cooper pairs allows many of the free electrons in the superconducting material to behave cooperatively. According to the theory, a superconductor has no electrical resistance because of the attractive interaction between its electrons that results in the formation of Cooper pairs. These electron pairs are bound to one another and flow without resistance around impurities and other imperfections. In an ordinary conductor, resistance occurs because its unbound electrons collide with imperfections and then scatter.
Scientists consider the BCS theory to be one of the most important contributions to theoretical physics since quantum mechanics began. Quantum mechanics is the field of physics that deals with the forces inside an atom and the motions of subatomic particles. The field originated in 1913 when Danish physicist Niels Bohr used the quantum theory to explain the motion of electrons in atoms. Bohr explained in terms of packets of energy called quanta how atoms absorb and radiate energy.
Cooper, Bardeen, and Schrieffer shared the 1972 Nobel Prize in physics “for their jointly developed theory of superconductivity, usually called the BCS theory.”
Superconductivity is used in the field of electromagnetics. Researchers have developed powerful superconducting magnets, which use much less electricity than ordinary electromagnets do. Superconducting magnets enable physicists to build more efficient particle accelerators, devices that speed up the movement of tiny bits of matter. These particles are either ions (electrically charged atoms) or electrically charged subatomic particles, objects that are smaller than an atom. The particles travel through an accelerator in a narrow beam. In accelerating the beam, the machine increases the particles' energy of motion. Physicists use accelerators to discover and study subatomic particles and the forces that govern them.
In 1958, Cooper moved to Brown University in Providence, Rhode Island, where he held several professorships. He made the unusual move of taking up research in theoretical biology, studying the behavior of the nervous system and developing special types of computer circuits that mimic animal nervous systems. Much of his work has been aimed at developing a theory of the central nervous system. In 1978, he became director of the Center for Neural Science at Brown. The Center was founded in 1973 to study animal nervous systems and the human brain. Cooper and his colleagues work toward an understanding of memory and other brain functions, aiming to formulate a scientific model of how the human mind works.
In 1975, Cooper helped found Nestor, Inc., to develop computer software and hardware systems called neural networks, which attempt to imitate the networks of nerve cells in the brain and its behavioral processes. Scientists working with this form of artificial intelligence are involved with designing computer systems that apply neural modeling concepts to technological problems. Such a computer system is not programmed in the same way as a conventional computer, but instead is designed to learn by example to recognize complex patterns. Nestor became an industry leader in applying neuralnetwork systems to commercial and military applications. By 2001, Nestor had become involved in video-based monitoring systems and services for traffic safety.
With a colleague, Cooper developed a software system that could recognize and transform handwritten letters into typed characters. The International Business Machines Corporation (IBM) introduced the system in 1987.
In 1991, Cooper became the first director of Brown University's Institute for Brain and Neural Systems. The institute brings together mathematicians, psychologists, engineers, physicists, linguists, computer scientists, and biologists to study the workings of the brains and nervous systems of the higher animals, including human beings.
Cooper has been awarded seven honorary degrees. He is a member of the American Academy of Arts and Sciences, the American Physical Society, the National Academy of Sciences, the American Philosophical Society, and a sponsor of the Federation of American Scientists. In 1968, along with Schrieffer, he was awarded the Comstock Prize of the National Academy of Sciences.