John Bardeen (Bardeen John)( The American physicist, Nobel Prize in Physics, 1956)
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Biography John Bardeen (Bardeen John)
May 23, 1908, Mr.. - 30 January 1991
American physicist and electrical engineer John Bardeen was born in g. Madison (Wisconsin), the son of Charles R. Bardeen, a professor of anatomy and dean of the medical school at the University of Wisconsin, and Elsie (nee Harmer) Bardin. After the death of the boy's mother in 1920. his father married Ruth Heims. Y B. has two brothers, sister and stepsister.
B. attended elementary school in Madison, skipping the fourth, fifth and sixth grades, and then entered the university high school, moved from her Madison Central High School, which he completed in 1923. Despite the congenital - tremor of the hands, in his youth he was a champion swimmer and skilful player in the pool.
At the University of Wisconsin B. received a bachelor's degree in electrical engineering in 1928, having studied as neprofiliruyuschih disciplines physics and mathematics. Another senior students, he worked in the engineering department 'Western Electric Company' (later the Division logged in laboratories of the company 'Bell'). In 1929, Mr.. He received a master's degree in electrical engineering from the University of Wisconsin, conducting research in applied geophysics and radiation antennas. The following year, he followed one of their leaders, American geophysicist, Leo J. Peters, in Pittsburgh (Pennsylvania), where the company 'Gulf rizerch' they have developed a new technique that allowed by analyzing maps of gravity and magnetic intensity, to determine the likely location of oil fields.
In 1933. B. enrolled at Princeton University, where he studied mathematics and physics under the direction of Eugen P. Wigner. He focused on the application of quantum theory to solid state physics. By that time, quantum mechanics is quite successfully describes the behavior of individual atoms and particles inside the atom. Solids are subject to the same quantum-mechanical laws, but as a macroscopic body is composed of a large number of atoms, objective analysis of its properties is much more complicated. Doctoral degree B. received in Princeton in 1936. for his thesis on the forces of attraction that keeps the electrons inside the metal. A year before the end of his dissertation, he accepted an offer to become a year after defending his fellows at Harvard University, and what remained until 1938. Harvard B. worked with John G. Van Vleck and P.U. Bridgman on problems of nuclear communications and electrical conductivity in metals.
When the specified period has ended, B. became an assistant professor at the University of Minnesota, where he continued his study of the behavior of electrons in metals. Between 1941 and 1945. He served as a civilian physicist naval artillery Laboratory in Washington (DC), studying the magnetic fields of ships - an important issue for those days, considering its application to the torpedo case and minesweeping.
In 1945, Mr.. B. joined the company 'Bell', where, working together with William Shockley and Walter Brattain, he managed to create semiconductors that can both straighten and strengthen the electrical signals. Semiconductors such as germanium and silicon - a material whose electrical resistance is intermediate between the resistances of the metal and insulator.
. In this process, Shockley tried to build what is now called MOSFET
. In this device the electric field induced by the voltage applied to the semiconductor, was to influence the movement of electrons inside the material. Shockley had hoped to use the electric field to control the free electrons in a section of the semiconductor and thereby modulate the current flowing through the device. In addition, the transistor had to have the potential to become the amplifier, since the small signal (applied voltage) can cause large changes in current flowing through the semiconductor.
. All attempts to construct the device by following this plan, ended in failure
. Then B. speculated that external pressure does not create the desired field within the semiconductor due to the layer of electrons at the surface. In further research revealed that the properties of the device depends on light, temperature, surface and changed by contact with body fluids or spraying on a semiconductor metallic film. In 1947, as the only group truly understood the surface properties of semiconductors, B. and Walter Brattain built the first working transistors.
One of the first was the point-contact transistor, made from a single piece of germanium. Point contacts were two thin 'antennae' of metal, called the emitter and collector, and attached to the top of the germanium block, the third contact, called the base, was connected with the lower part of the block. To control the current between the emitter and collector used a small current flowing between the emitter and base. This idea has replaced the original idea of control by an external electric field. In a later version, called planar transistor, point contacts have been removed, and the emitter and collector were formed from semiconductor materials, which are interspersed with small amounts of specific impurities. Field effect transistors could find practical application until Germany has been replaced by silicon as the basic material.
. Like tubes, transistor allows using a small signal (voltage for the lamp current for a transistor) in a circuit to control a relatively large current in another circuit
. Due to small size, . simple structure, . low energy requirements and low cost of fast transistors replaced vacuum tubes in all of radio devices, . except for high power devices, . used, . example, . in broadcasting or radio frequency heating of industrial plants,
. Currently, all high-speed wireless devices, as well as many high-power high-frequency units, where you can do without electron tubes, commonly used bipolar transistors. Improved technology has made possible the creation of many transistors from tiny pieces of silicon that could perform more complex functions. The number of transistors in one such piece has grown from 10 to about 1 million, in particular by reducing the size of connections and the transistors themselves to the size of half a micron to several microns (a micron equals 0.001 mm). These pieces can build modern computers, communications and management, and technology continues to develop rapidly.
B. divided in 1956. Nobel Prize with William Shockley and Walter Brattain 'for the study of semiconductors and the discovery of the transistor effect'. 'Transistor largely exceeds Tubes', - said EG. Rudberg, a member of the Royal Swedish Academy of Sciences, at the presentation of the winners. Pointing, . that the transistors are much smaller than electron tubes, and unlike the latter does not require electric current to the filament yarn, . Rudberg added, . that 'for acoustic instruments, . computers, . exchanges and much more is required just such a device '.,
. In 1951, Mr.
. Bardeen left the telephone company 'Bell' and accepted the offer to occupy simultaneously two posts: Professor of Electrical Engineering and professor of physics at the University of Illinois. Here he resumed serious interest in the subject, which he was engaged in postgraduate years, and which was interrupted by World War II and did not resume them until 1950 - the problem of superconductivity and the properties of matter at very low temperatures.
. Superconductivity was discovered in 1911
. Netherlands physicist Kamerlingh Onnes, who discovered that certain metals completely lose their resistance to electric current at temperatures a few degrees above absolute zero. Electric current is a stream of electrons moving in a certain direction.
. In metals, many electrons are so loosely connected with the atoms, that the electric field induced by an external voltage, forcing them to move in the direction of the field
. However, the electrons also oscillate in random directions because of the heat. This movement causes the scattered opposition (resistance) flow of electrons under the influence of the field. As a result of cooling the thermal motion decreases, the resistance also decreases. At absolute zero, where thermal motion ceases altogether, we can expect that resistance will disappear altogether. However, absolute zero is practically unattainable. Surprisingly superconductivity in the fact that resistance disappears at a temperature somewhat higher than absolute zero, when there is more thermal motion. No satisfactory explanation for this finding did not succeed.
It was found that superconductors have another unusual characteristic, opened in 1933. German physicist Walter Meissner. He found that they are committed diamagnets, ie. prevent the penetration of the magnetic field inside the metal. Paramagnetic materials, among which are the usual magnetic metals such as iron, more or less amenable to magnetization of a nearby magnet. Since the magnetic field of the magnet induces a field of opposite direction in the paramagnetic body, this body is attracted to a magnet. But as a diamagnetic body counteracts the magnetic field, this body and a magnet repel each other, regardless of which one pole of a magnet we bring to it. A magnet placed above the superconductor will be based 'on a cushion of magnetic repulsion'. However, if the applied magnetic field is large enough, the superconductor loses its properties and behaves like an ordinary metal. In 1935. German physicist Fritz London has suggested that diamagnetism is a fundamental property of superconductors and that the superconductivity may represent a certain quantum effect that manifests itself in some way throughout the body.
. Signs that F
. London was on the right track, appeared in 1950, Mr.. Several U.S. physicists have found that different isotopes of the same metal becomes superconducting at different temperatures and that the critical temperature is inversely proportional to the atomic mass. Isotopes are forms of an element, . having the same number of protons in their nuclei (and, . hence, . same number of electrons surrounding the nucleus) and chemically similar to each other, . but their nuclei contain different numbers of neutrons and, . hence, . have different masses,
. B. knew that the only effect of different atomic masses on the properties of a rigid body is manifested in the differences in the distribution of vibration within the body. Therefore, he suggested, . that the superconductivity of the metal involved interaction between mobile electrons (which are relatively free, . so that they can move, . forming an electric current) and the vibrations of metal atoms and that as a result of the interaction of electrons creates a link with each other.,
. To study B
. later joined by two of his students at the University of Illinois - Leon H. Cooper, who led the research post-doctoral fellow, and J. Robert Schrieffer, a graduate student. In 1956, Mr.. Cooper showed, . that the electron (which carries a negative charge), . moving through the regular structure (grating) of the metal crystal, . attracts positively charged atoms coming, . slightly deform the grid and creating a short-term increase in the concentration of positive charge,
. This concentration of positive charge in turn attracts a second electron and two electrons form a pair, linked to each other through the distortion of the crystal lattice. In this way, many of the electrons in the metal are united by two, forming Cooper pairs.
B. Schrieffer and tried using the concept to explain the behavior of Cooper's vast population of free electrons in a superconducting metal, but they were unsuccessful. When B. in 1956. went to Stockholm to receive the Nobel Prize, Schrieffer was ready to admit defeat, but summing B. fuse into his soul, and he has yet to develop statistical methods needed to solve the problem.
. After that, B., Cooper and Schrieffer were able to show that Cooper pairs interacting with each other, forcing many of the free electrons in a superconductor move in unison, a single stream
. As surmised F. London, superconducting electrons form a quantum state, covering all metal body. The critical temperature at which superconductivity occurs, determines the degree of reduction of temperature fluctuations, when the effect of Cooper pairs to coordinate the movement of free electrons becomes the dominant. Since the emergence of resistance in the rejection of even a single electron from the total flow with the need to affect other electrons, . participating superconductivity, . and thereby disrupt the unity of the quantum state, . such indignation is highly unlikely,
. Therefore, the superconducting electrons move collectively, without loss of energy.
Achieving B., Cooper and Schrieffer was named one of the most important in theoretical physics from the inception of quantum theory. In 1958, Mr.. they are using his theory of superfluidity is predicted (the absence of viscosity and surface tension) of liquid helium-3 (an isotope of helium, . whose nucleus contains two protons and one neutron) near absolute zero, . that was confirmed experimentally in 1962,
. Superfluidity observed earlier in the helium-4 (the most common isotope with one extra neutron), and it was thought that it is impossible for the isotopes with an odd number of nuclear particles.
B., Cooper and Schrieffer divided in 1972. Nobel Prize in Physics "for the joint development of the theory of superconductivity, usually called the BCS theory '. Stig Lundqvist, . Member of the Royal Swedish Academy of Sciences, . presentation of the laureates said in the full explanation of superconductivity, and added: "Your theory has predicted new effects and highly stimulated further developments in theoretical and experimental studies',
. He also pointed out that 'further development ... confirmed the great importance and value of the ideas embodied in this fundamental work in 1957 '
BCS theory has had far-reaching consequences in the technology and theory. Creation of materials that become superconductors at higher temperatures and withstand strong magnetic fields, allowed to construct a very powerful electromagnets small size, low power consumption. The magnetic field produced by an electromagnet is directly related to the current in its windings. For a regular presence of the wire resistance is a serious limitation because the heat emitted is proportional to the square of the resistance and amperage. It's not just that the heat loss is spent on expensive energy, but also wears out the material. Superconducting magnets are used in the study of nuclear fusion, . in magnetohydrodynamics, . in high-energy particle accelerators, . in trains, . moving without friction on a magnetic cushion above the rails, . in biological and physical studies of the interaction of atoms and electrons with magnetic fields, and in the design of compact high-power generators,
. English physicist Brian D. Josephson discovered that under certain conditions when connecting superconductors arise so-called supercurrent (Josephson effect), sensitive to magnetic fields. Sensors based on the Josephson effect, are able to identify the smallest changes of magnetic activity in living organisms and help to detect mineral deposits and oil on their magnetic properties.
In 1959, Mr.. B. started working at the Center for Basic Research University of Illinois, continuing his studies in the field of solid state physics and low temperature physics. In 1975. He became an honorary professor emeritus.
B. married Jane Maxwell in 1938, they have two sons and a daughter. In his spare time he travels and plays golf.
Among the numerous awards B. - Medal Stuart Ballantyne Franklinovskogo Institute (1952), Mr. John Scott Award. Philadelphia (1955), . Prize in solid state physics Oliver Buckley, the American Physical Society (1954), . National Medal 'For his scientific achievements' of the National Science Foundation (1965), . Medal of Honor of the Institute of Electrical and Electronics Engineers (1971) and the Presidential Medal of Freedom United States Government (1977),
. For many years, B. was co-editor of the journal 'Physical Review'. He is a member of the U.S. National Academy of Sciences and the American Academy of Arts and Sciences and was elected a member of the American Physical Society.