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Doerte Blume - Zoom Public Talk - Advanced Studies Gateway at FRIB

Helium: from an extremely weakly-bound molecule to superfluidity

Helium is the only element that remains liquid under normal pressure down to zero temperature. Below 2.17K, bulk helium-4 is superfluid. Motivated by this intriguing behavior, the properties of finite-sized helium droplets have been studied extensively over the past 30 years or so. Some properties of liquid helium-4 droplets are, just as those of nuclei, well described by the liquid drop model. The existence of the extremely fragile helium dimer was proven experimentally in 1994 in diffraction grating experiments. Since then, appreciable effort has gone into creating and characterizing trimers, tetramers and larger clusters. The excited state of the helium trimer is particularly interesting since it is an Efimov state. The existence of Efimov states, which are unique due to scale invariance and an associated limit cycle, was predicted in 1971. However, till 2015, Efimov states had -- although their existence had been confirmed experimentally -- not been imaged directly. Ingenious experimental advances that utilize femtosecond lasers have made it possible to directly image the static quantum mechanical density distribution of helium dimers and trimers. This talk will highlight recent experimental and theoretical work on the helium dimer, helium trimer, and helium droplets.

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Jan 8, 2023 01:00 PM in Eastern Time (US and Canada)