David Lee was born in Rye, New York, on January 20, 1931, the son of Marvin Lee and Annette (Franks) Lee. After earning a B.A. at Harvard University in 1952, Lee served in the U. S. Army until 1954. The following year, he completed his M.S. at the University of Connecticut. In 1959, having received his Ph.D. from Yale University, Lee joined the Department of Physics at Cornell University as an instructor; he was named professor of physics in Cornell's College of Arts and Sciences in 1968.
Low-temperature physics, Lee's field, explores the behavior of materials at very low temperatures, almost at absolute zero, the lowest temperature possible, 0 K (Kelvin), equalling -459.67°F (-273.15°C). Quantum mechanics, formulated in the context of quantum theory, and based on the concept of a particular quantity, or quantum, of energy needed to effect a change, enables scientists to explain phenomena, such as the behavior of subatomic particles, which defy classical mechanics. Even in the unusual and mysterious world of quantum physics, where strange phenomena seem to be the rule rather than the exception, low-temperature, or condensed-matter, physics apparently enjoys a special status. Physicists who explore this area are creating conditions that have never existed anywhere in the universe. Indeed, as researchers have discovered, in the separate universe of cryogenics, liquids reach the state of superfluidity, exhibiting such properties that can hardly be imagined in the world of "normal" liquids. For example, superfluids, because their atoms have stopped moving in a random fashion, lose all inner friction, and, as a result, appear uncontainable. In other words, left in a container, a superfluid will spontaneously overflow it.
Interestingly, when Lee and his colleagues at Cornell (Richardson was a fellow-senior researcher, while Osheroff was a graduate student) embarked on their study of helium-3, in the late 1960s, superfluidity was not their goal. Instead, they were searching for a phase transition--which in the macroscopic world, for example, would refer to the transition of a body from a solid to a liquid state--of frozen helium-3 to a magnetic order. However, the series of experiments that Lee and his collaborators conducted on frozen helium-3 eventually led to the discovery--reported in 1972--of superfluidity in helium-3. In fact, the scientists eventually found that superfluid helium-3 occurs in two different superfluid states.
In order to appreciate the magnitude of this discovery, it is necessary to explain the difference between the two isotopes of helium, Helium-4 and Helium-3. A common isotope, helium-4, also called a boson, has a nucleus, consisting of two protons and two neutrons, and two electrons. Bosons, which have an even number of particles, behave in accordance with Bose-Einstein condensation, in which a significant amount of particles are in the lowest-energy single quantum state. Consequently, helium-4 reaches the state of superfluidity at 2.17 K, which was confirmed experimentally in the 1930s by the Russian physicist Pyotr Leonidovich Kapitza, who, incidentally, coined the term superfluid. However, helium-3, called a fermion because of its unique structure (nucleus consisting of one neutron and two protons; two electrons) seemed impossible to bring to a superfluid state. For decades following the discovery of the superfluidity of helium-4, researchers, realizing that Bose-Einstein condensation does not work for fermions, assumed the helium-3 would always resist efforts to make it superfluid. Indeed, Lee and his team cooled the Helium-3 ice to 2.7 millikelvins, which means the temperature of superfluid helium-4 is roughly a thousand times higher than that of helium-3 in a superfluid state.
A remarkable breakthrough in condensed-matter physics, the discovery made by Lee and his colleagues also has profound implications for cosmology. Namely, scientists have connected Helium-3 superfluidity with the creation of cosmic strings, which may have played a role in the formation of galaxies. According to scientists, cosmic strings, whose existence is hypothetical, may have emerged in the wake of phase transitions a fraction of a second after the Big Bang. Experiments in which superfluid helium-3 was rapidly heated and subsequently cooled yielded vortices which are believed to correspond, on a microscopic scale, to cosmic strings. These events involving helium-3 may replicate, scientists believe, the birth of our universe.
For their efforts, Lee and his colleagues (Robert C. Richardson and Douglas D. Osheroff) shared the 1996 Nobel Prize for Physics for their discovery of superfluidity in helium-3, a rare isotope of helium. Lee, highly esteemed for his pioneering work in cryogenics, the physics of extremely low temperatures, has also investigated the effects of low temperatures on metals and other materials.
Lee is Cornell University, doing research for the school's Laboratory of Atomic and Solid Physics.
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