Anthony J. Leggett, who shared the Nobel Prize in Physics in 2003 for discovering that the anomalies in his colleagues’ experiments were in fact signs of a scientific breakthrough — that the rare gas helium-3 had transformed into a superfluid, a state in which a liquid can climb up and over the walls of a container without friction or loss of kinetic energy — died on Sunday at his home in Urbana, Ill. He was 87.
His death was confirmed by his colleague Smitha Vishveshwara, a physics professor at the University of Illinois Urbana-Champaign.
In June 1972, Robert C. Richardson, an experimental physicist at Cornell University, was visiting England and passing through the University of Sussex, where Dr. Leggett was a professor, when he asked to speak with him. Dr. Richardson wanted to discuss some puzzling results that he and two of his Cornell colleagues, David M. Lee and Douglas Osheroff, had obtained from experiments on freezing helium-3, a rare type of helium that is very difficult to work with at low temperatures. Its far more common cousin, helium-4, is the gas often used to make balloons float.
In the late 1930s, the Soviet physicist Pyotr Kapitsa and, independently, the Canadian physicist John F. Allen and his student Don Misener discovered that when helium-4 is cooled to minus 455.76 degrees Fahrenheit (about four degrees above absolute zero, the temperature at which atoms theoretically become motionless), it becomes a superfluid.
In the following decades, scientists tried repeatedly to cool helium-3 down into a superfluid, but without success. Some began to believe that it was not possible.
Dr. Lee, Dr. Osheroff and Dr. Richardson gave it a shot, with the goal of uncovering magnetic fields in helium-3 in the process.
To do so, they simultaneously lowered the temperature and increased the pressure on helium-3. As they did so, they noticed small, unexpected jumps in the pressure readings, but they assumed that they had merely stumbled on a phase transition — that the gas had become a solid, like ice
They published a preliminary paper on their findings. But as Dr. Leggett studied their results, he came to a different conclusion: that the helium-3 had gone through not one phase transition but two, a never-before-seen phenomenon. Instead of turning into a solid, helium-3 had become a liquid, specifically a superfluid.
He issued two papers in the journal Physical Review Letters, one in October 1972 and another in August 1973, explaining his hypothesis and offering other scientific predictions. The second paper further proved that the three Cornell scientists had discovered superfluid helium-3.
For their discovery, Dr. Richardson, Dr. Lee and Dr. Osheroff were awarded the Nobel Prize in 1996. In the citation, the Nobel committee said that Dr. Leggett’s contribution had been particularly important “in the interpretation of the discovery.”
Seven years later, Dr. Leggett received his own Nobel recognition from the Royal Swedish Academy of Sciences, along with Alexei A. Abrikosov and Vitaly L. Ginzburg, for “pioneering contributions to the theory of superconductors and superfluids.”
In its citation about Dr. Leggett’s work, the Nobel committee said that his insights had proved useful in explaining phenomena in cosmology, such as reactions in neutron stars, and in cracking the code of how turbulence occurs in nature, “one of the last unsolved problems in classical physics.”
As Dr. Osheroff told The New York Times that year, Dr. Leggett’s theories of helium-3 superfluidity were “really a key piece” of his colleagues’ Nobel-winning work. Several times when they observed a new effect in the substance, he said, “sure enough, Tony had predicted it.”
Anthony James Leggett was born on March 26, 1938, in Camberwell, an area of South London, and moved a little farther south to Upper Norwood soon after. He was the eldest of five children of Richard Dominic Leggett, a high school teacher of physics, chemistry and math, and Winifred Kathleen (Regan) Leggett, who briefly taught mathematics before leaving to raise a family.
At the start of War World II, the family moved to Englefield Green, west of London, and Anthony attended the local Catholic school. When he was 13, his family returned to Upper Norwood, and he transferred to Beaumont College, a private Jesuit school, where his father taught.
As one of Beaumont’s top students, Anthony was steered into classics, considered the most prestigious area of study. But he caught the attention of Charles O’Hara, a retired priest and former university lecturer in mathematics, who began tutoring Anthony privately, providing him with an invaluable foundation for his later studies in physics.
While finishing his undergraduate education at Oxford University, majoring in classics, he decided that he wanted to be a physicist.
His decision was fueled by a desire “to make meaningful conjectures about the way the world works,” Dr. Leggett said in 2021 in an oral history interview for the Federal University of Pará in Brazil.
But he had never truly studied the subject; he had attended a few classes in high school, he said, but had found that the lessons “went in one ear and out the other.”
Meanwhile, military service loomed: Having deferred mandatory service to pursue his undergraduate degree, he could not defer it again.
Fortunately for him, though, the Soviet Union’s launch of the world’s first artificial satellite, Sputnik, in October 1957 had sent the western world into a tizzy of hand-wringing about its scientific readiness. Scientists were suddenly in high demand, and Dr. Leggett saw an opportunity.
The Oxford faculty “were able to convince the draft board that I’d be more use to the country doing a second degree in science rather than on the parade ground,” he recalled in an interview with the Perimeter Institute for Theoretical Physics in 2024.
After completing his undergraduate degree in physics in two years, also at Oxford, he stayed on for a Ph.D., which he received in 1964, focusing on phenomena in liquid helium.
Dr. Leggett spent the 1964-65 academic year as a postdoctoral researcher at the University of Illinois Urbana-Champaign, working partly under Dr. John Bardeen, who won the Nobel in Physics in 1956 and 1972, and under David Pines, a noted theorist. Dr. Leggett then went to Japan to work for a year under the Japanese physicist Takeo Matsubara at Kyoto University.
He was hired by the University of Sussex in 1967 and spent the next 15 years there, taking a break only to teach a semester in 1976 and again in 1977 at the University of Science and Technology in Kumasi, Ghana.
Around the time of his fateful meeting with Dr. Richardson in June 1972, Dr. Leggett married Haruko Kinase, whom he had met while she was an undergraduate student at Sussex.
He is survived by his wife, Dr. Kinase-Leggett, who has a doctorate in anthropology; their daughter, Elizabeth Asako Kinase-Leggett; and his younger sisters, Judith Leggett and Clare Prangley. His younger brothers, Terence and Paul, both died.
Dr. Leggett joined the Illinois faculty at Urbana-Champaign in 1983. There, he became interested in a new problem: how to resolve the paradox between quantum physics and mechanical physics, in which rules that apply to one system do not apply to the other.
Studying a specific facet of that paradox, Dr. Leggett and a graduate student, Amir Caldeira, constructed a model based on earlier work by the physicists Richard Feynman and Frank Lee Vernon Jr. to explain the dissipation of energy in quantum physics.
The Caldeira-Leggett model has become one of the leading areas of research and testing in an area of physics known as quantum dissipation.
Looking back on his life, Dr. Leggett called the launch of Sputnik the “most serendipitous event” in his career. In his interview with the Perimeter Institute, he explained: “The cry went up, ‘How come that the Soviets have got ahead of us in this incredibly important technological field?’ And, of course, the answer was, ‘Well, we’ve encouraged all our best people to go into useless things like classics and not into useful things like physics.’”
Ash Wu contributed reporting.
The post Anthony J. Leggett Dies at 87; Won Nobel for Theories on Superfluids appeared first on New York Times.
