Goldstone mode and pair-breaking excitations in atomic Fermi superfluids

Sascha Hoinka, Paul Dyke, Marcus G. Lingham, Jami J. Kinnunen, Georg M. Bruun, Chris J. Vale*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

34 Citations (Scopus)


Spontaneous symmetry breaking is a central paradigm of elementary particle physics1, magnetism2, superfluidity3 and superconductivity4. According to Goldstone's theorem, phase transitions that break continuous symmetries lead to the existence of gapless excitations in the long-wavelength limit. These Goldstone modes can become the dominant low-energy excitation, showing that symmetry breaking has a profound impact on the physical properties of matter. Here, we present a comprehensive study of the elementary excitations in a homogeneous strongly interacting Fermi gas through the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC) of molecules using two-photon Bragg spectroscopy. The spectra exhibit a discrete Goldstone mode, associated with the broken-symmetry superfluid phase, as well as pair-breaking single-particle excitations. Our techniques yield a direct determination of the superfluid pairing gap and speed of sound in close agreement with strong-coupling theories.

Original languageEnglish
Pages (from-to)943-946
Number of pages4
JournalNature Physics
Issue number10
Publication statusPublished - 4 Oct 2017
MoE publication typeA1 Journal article-refereed

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    Hoinka, S., Dyke, P., Lingham, M. G., Kinnunen, J. J., Bruun, G. M., & Vale, C. J. (2017). Goldstone mode and pair-breaking excitations in atomic Fermi superfluids. Nature Physics, 13(10), 943-946.