Goldstone mode and pair-breaking excitations in atomic Fermi superfluids

Research output: Contribution to journalArticleScientificpeer-review


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

Research units

  • Swinburne University of Technology
  • Aarhus University


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

ID: 15848182