Frogs, timetables and the weather
David Morris Lee was born on January 20, 1931, in Rye, New York, a small town just outside New York City. His parents, Marvin Lee, an electrical engineer, and Annette Franks Lee, an elementary school teacher, were born and raised in New York City, the children of Jewish immigrants who had come from England and Lithuania in the late 1800s. His father commuted to a small electrical manufacturing company in the city and rose to become its president. During the Depression the family moved into the city for a few years to save money before returning to Rye.
As a boy Lee roamed the fields and shoreline collecting frogs, fish, salamanders and snakes, spent summers at camps in New England, and collected railway timetables for the whole country until he was a young travel expert. As a young teenager he kept his own weather records and subscribed to the daily weather map. One day he picked up a book from his father’s shelf, The Mysterious Universe by Sir James Jeans, which his father said no one really understood. Its account of cosmology fascinated him and, he believed, sparked his interest in physics.
Harvard, the Army and a conversation on guard duty
Lee graduated from Rye High School in 1948 and studied physics at Harvard, where he also took pre-medical courses and sailed in the 1950 Bermuda Race with the Harvard Yacht Club. He graduated in January 1952 and served 22 months in the U.S. Army during the last stages of the Korean War. One night, as corporal of the guard, he fell into conversation with a young soldier named Herbert Fried, who had studied the theory of superfluidity. Their talk about superfluid helium helped send Lee to the University of Connecticut, where he earned a master’s degree and met Charles Reynolds and John Reppy, who fired his interest in low-temperature physics.
In 1955 he entered the doctoral programme at Yale, where under Henry Fairbank he studied liquid helium-3, a rare light form of helium that had only just become available in usable amounts. He completed his PhD in 1959.
His first summer project at Yale was building a mercury-jet stripper for a heavy-ion accelerator, a device that strips electrons from ions so they can be accelerated harder. That summer he also helped Russell Donnelly with experiments on rotating superfluid helium, and in a short time, he recalled, he learned a great deal about experimental low-temperature physics and the life of an experimental physicist. He found it totally rewarding to see new effects in an apparatus he had designed and built with his own hands.
Building a laboratory at Cornell
In January 1959 Lee joined the faculty of Cornell University in Ithaca, New York, with the job of setting up a low-temperature research laboratory, teaching physics and running the helium liquefier. Soon after arriving he met Dana, a doctoral student in nutrition and biochemistry who was born and raised in Thailand; they married and have two sons. Over the following decade the Cornell low-temperature group grew with the arrival of John Reppy and Robert Richardson, and it became one of the best in the world.
The group’s aim was to reach temperatures within a few thousandths of a degree of absolute zero, the point at which all heat motion stops. At such temperatures matter stops behaving according to everyday rules, and the strange laws of quantum mechanics show themselves on a scale large enough to see.
Two kinds of helium
To see why helium-3 mattered, it helps to know that helium comes in two natural forms. Common helium-4 has a nucleus of two protons and two neutrons; with its two electrons it contains an even number of particles, which makes it what physicists call a boson. Bosons can crowd together into a single lowest-energy state, and when liquid helium-4 is cooled to 2.17 degrees above absolute zero it does just that, becoming a superfluid, as Pyotr Kapitza discovered in the 1930s.
Helium-3, with only one neutron, contains an odd number of particles and is a fermion. Fermions obey a strict rule that no two can share the same state, so helium-3 should not be able to condense in the same way. But the theory of superconductivity, worked out by John Bardeen, Leon Cooper and Robert Schrieffer, showed how electrons, which are also fermions, can pair up in a cold metal and behave together like bosons. If helium-3 atoms could pair in the same way, the liquid might become a superfluid at some far lower temperature. Finding out required reaching temperatures a thousand times colder than those at which helium-4 turns superfluid, and that was exactly what Lee had built his laboratory to do.
Kinks in a pressure curve
Ordinary helium, helium-4, becomes a superfluid at about two degrees above absolute zero: it loses all internal friction, creeps up the walls of its container and flows through holes too small for any normal liquid. Helium-3 atoms are different. Because each has an odd number of particles, quantum rules forbid them from simply piling into the same lowest-energy state. The theory of superconductivity suggested they might do so by pairing up, as electrons do in a superconductor, but many groups had searched without success through the 1960s.
Lee, Richardson and their graduate student Douglas Osheroff were actually looking for something else: a magnetic transition in frozen helium-3. They used a Pomeranchuk cell, which cools helium-3 by squeezing it so that part of it freezes. In November 1971 Osheroff noticed small kinks in the curve of pressure against time. Rather than dismiss them as quirks of the apparatus, the team investigated. Their first paper, in 1972, attributed the effect to the solid. Further measurements that same year showed that it came from the liquid, which passed through two new phase transitions about two thousandths of a degree above absolute zero. Helium-3 had become a superfluid, and the Cornell team soon found it had more than one superfluid phase.
Groups elsewhere, including Olli Lounasmaa’s in Helsinki, quickly confirmed that the new liquid flowed without friction. Lee, Osheroff and Richardson shared the 1996 Nobel Prize in Physics for the discovery.
What the discovery gave science
Superfluid helium-3 turned out to be one of the richest systems in physics: a liquid whose atoms pair up in a complex way, with properties that differ by direction like a liquid crystal and vortices of many shapes. It became a test bed for theories that apply far beyond helium, from superconductors to the neutron stars left behind by exploding stars. In 1996 two research teams used it to test, in the laboratory, a theory of how cosmic strings might have formed in the early universe. As the Nobel committee put it, the discovery showed that the quantum laws of microphysics sometimes directly govern the behaviour of large bodies.
The Cornell group’s wider work also mattered. Lee, Reppy and graduate student Erlend Graf discovered the tricritical point in mixtures of helium-3 and helium-4, the point at which their behaviour on separating into two liquids changes character. That separation is what powers the dilution refrigerator, the machine scientists use to cool experiments, and today the superconducting quantum computers being built by companies and laboratories, to a few thousandths of a degree above absolute zero. Lee’s group also discovered magnetic ordering in solid helium-3 and, with chemist Jack Freed, nuclear spin waves in a gas of spin-polarised hydrogen.
Other members of the group made their own discoveries in the same laboratory: John Reppy and his student David Bishop provided a striking demonstration of the Kosterlitz-Thouless transition in thin films of superfluid helium-4, a phenomenon recognised by the 2016 Nobel Prize in Physics, and Jeevak Parpia studied superfluid helium-3 confined in tiny spaces.
A Jewish family from Rye
Lee is the grandson of Jewish immigrants from England and Lithuania, one of whose great-grandfathers had settled in the United States earlier still. His family’s path, from immigrant grandparents to a father who rose from engineer to company president, and from a public high school to Harvard, is a familiar one in American Jewish history. He has not written publicly about religious practice. He is counted among Jewish Nobel laureates in physics.
Teacher and colleague
Lee has always said that one of the greatest rewards of his career was working with graduate students and watching them succeed, and he named Douglas Osheroff, his former student, as a prime example. He became professor emeritus at Cornell in 2007 and in 2009 joined Texas A&M University as a distinguished professor of physics, where he has continued research. He received the Sir Francis Simon Memorial Prize in 1976 and the Oliver Buckley Prize in 1981, both shared with Osheroff and Richardson, and he is a member of the National Academy of Sciences and the American Academy of Arts and Sciences. In 2008 he joined other American physics laureates in urging the U.S. government to restore funding for basic research.
He still enjoys hiking in the mountains, a love he took up when John Reppy, an expert climber, coaxed him past his fear of heights in the Grand Tetons.
Legacy
David Lee’s legacy is a laboratory and a way of working: build your own apparatus, push to colder temperatures than anyone else, and take seriously the small anomalies that others might ignore. The superfluid his group found is now in physics textbooks, and the techniques developed in low-temperature laboratories like his have become part of the infrastructure of modern science and of the emerging technology of quantum computing.
Sources & further reading
David M. Lee, Biographical, NobelPrize.org · Press release: The Nobel Prize in Physics 1996, NobelPrize.org · David Lee (physicist), Wikipedia · Dilution refrigerator, Wikipedia · Superconducting quantum computing, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.