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Low-temperature physics

Surprise in the strong regime

Nature volume 463, pages 1029–1030 (2010)Cite this article

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The finding that the normal phase of an ultracold gas of fermionic atoms in the strongly interacting regime is close to a Fermi liquid isn't quite what theorists expected for these systems.

During the past decade, ultracold gases of fermions (particles with half-integer spin, such as electrons) gained renown as a tool for modelling the physics of strongly interacting many-body systems. In the vicinity of a Feshbach resonance, these systems can be conveniently controlled with a magnetic field to reach the unitary limit, the point at which the interactions between particles become strongest and the thermodynamic properties of the system become universal — that is, independent of the nature of the interactions1. As such, ultracold Fermi gases with tunable interactions allow us to probe the crossover from the Bardeen–Cooper–Schrieffer (BCS) superfluid state, which describes the frictionless flow of weakly interacting electron pairs in superconductors, to the Bose–Einstein condensate (BEC) superfluid state, which occurs in systems made of bosons (particles with whole-integer spin) such as helium-4 (ref. 2); the gas's weakly interacting fermions can be made to interact strongly and bind together into bosonic molecules that ultimately condense into a BEC. On page 1057 of this issue, Nascimbène et al.3 provide insight into the strongly interacting, BCS–BEC crossover regime by devising an experiment that yields the equation of state for a unitary Fermi gas.

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Figure 1: Nature of the strongly interacting regime.

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  1. Yong-il Shin is in the School of Physics and Astronomy, Seoul National University, Seoul, 151-747, Republic of Korea. yishin@snu.ac.kr ,

    Yong-il Shin

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  1. Yong-il Shin
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Shin, Yi. Surprise in the strong regime. Nature 463, 1029–1030 (2010). https://doi.org/10.1038/4631029a

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