2. The discovery
Superfluidity in helium-3 first manifested itself as small anomalies in the melting curve of solid helium-3, i.e. as small structures in the diagram representing pressure against time, when the fluid was cooled. It is always tempting to consider small deviations as more or less inexplicable peculiarities of the equipment, but the discoverers became convinced that there was a real effect. They were actually not looking for superfluidity, but for an antiferromagnetic phase in solid helium-3, which according to predictions was to appear below 2 mK. It was thus natural that they, in their first publication 1972, interpreted the effect as the observation of such a phase transition.
The agreement was not perfect, but by further development of their technique and new measurements they could, just a few months later, pinpoint the effect. It actually turned out to involve two phase transitions in the liquid phase, at 2.7 and 1.8 mK respectively.
The discovery became the starting point of an intense activity among low temperature physicists. The experimental and theoretical developments went hand-in-hand in an unusally fruitful way. The field was rapidly mapped out, but fundamental discoveries are still being made.