Today Douglas Osheroff discussed his view of “How Advances in Science are Made” at the 62nd Lindau Nobel Laureate Meeting. Some days before the meeting I had a short email conversation with him, where we chatted about his finding, the need of interdisciplinarity of sciences and how he advanced in science. Osheroff was awarded the Nobel Prize for Physics in 1996 together with David M. Lee and Robert C. Richardson “for the discovery of superfluidity in Helium 3”.
Superfluid liquids continue to flow without any friction. Since 1911 researchers had known that helium 4 had such a superfluid phase close to absolute zero. According to the Barden-Cooper-Schriefer (BCS) theory for the explanation of superconductivity (Nobel Prize for Physics 1972), it was to be expected that helium 3 could also achieve the superfluid state under certain conditions – the formation of a so-called Cooper Pair.
Doctoral student Douglas Osheroff confirmed this through his presence of mind one night in April 1972. He investigated the magnetic properties of solid helium 3 only 0.2 degrees above absolute zero at Cornell University in Ithaca. His aim was to record a so-called phase shift by increasing the pressure as a function of time. However, he noticed unexpected jumps in the measurement curves and realized that this almost certainly the superfluid phase transition in liquid 3He.
In that night in April 1972 you say unexpected effects in your measurements. How long took it to put the puzzle together and to find out that your data fitted to the predicted suprafluidity.
We were trying to understand the nature of nuclear spin order in solid 3He along the melting curve. Our refrigeration process was based on the adiabatic solidification of liquid 3He along the melting curve. We did not expect to find ordering in the liquid state, but because we had both solid and liquid in our cell, we could see the properties of both phases.
In the night that I discovered the two phase transitions in the liquid I wrote in my lab book:
I have invented an early from of MRI (Magnetic Resonance Imaging), and so I could differentiate the liquid from the solid NMR signals. The liquid NMR signal dropped by about a factor of two at the lower temperature transition. I felt that this had to be the result of the formation of ‘Cooper Pairs’ in the liquid.
What did you do next in that night?
David Lee was my thesis advisor, and so it made sense for me to call him. Bob Richardson had his own student, Bill Halperin, who was doing similar experiments. However, it was Bob who largely trained me in low temperature physics. This was in the middle of the night, and I didn’t even call my wife.
Apart from the fascinating discoveries in basic research, what can superfluidity be used for today? What other findings are associated with it?
Superfluidity in 3He was the first example of an ‘unconventional’ BCS state. It taught us a lot about what states were possible, and what properties they might exhibit. However, because of the extremely low temperatures needed to create superfluidity in 3He, it has no practical applications.
Networking and interdisciplinarity seem to be necessary new discoveries.
Yes. I think I owe a great deal to Ed Hammel. He was responsible for keeping the Nation’s tritium supply clean during the period when the US and the USSR were trying to build a hydrogen bomb. Tritium decays to 3He with a half life of 12.4 years. So periodically Hammel would separate out the 3He from the tritium. But he saved the 3He, and eventually liquified the 3He. He published his results, and even said how much 3He he had liquified. In a telephone interview he confided to me that this told the Russians not only something about how much Tritium the US had, but something about how long we had had it. He was for sure the father of 3He physics!
Can one plan advances in science?
I would say that most advances require both insight and good fortune. I was attracted to the low temperature group at Cornell because it seemed to give me the opportunity to look at Nature in a new and very different realm.