Strong-Coupling Effects and Shear Viscosity in an Ultracold Fermi Gas

D. Kagamihara, Y. Ohashi

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


We theoretically investigate the shear viscosity η, as well as the entropy density s, in the normal state of an ultracold Fermi gas. Including pairing fluctuations within the framework of a T-matrix approximation, we calculate these quantities in the Bardeen–Cooper–Schrieffer (BCS)–Bose–Einstein condensation (BEC) crossover region. We also evaluate η/ s, to compare it with the lower bound of this ratio, conjectured by Kovtun, Son, and Starinets (KSS bound). In the weak-coupling BCS side, we show that the shear viscosity η is remarkably suppressed near the superfluid phase transition temperature Tc, due to the so-called pseudogap phenomenon. In the strong-coupling BEC side, we find that, within the neglect of the vertex corrections, one cannot correctly describe η. We also show that η/ s decreases with increasing the interaction strength, to become very close to the KSS bound, ħ/ 4 πkB, on the BEC side.

Original languageEnglish
Pages (from-to)692-698
Number of pages7
JournalJournal of Low Temperature Physics
Issue number5-6
Publication statusPublished - 2017 Jun 1


  • BCS–BEC crossover
  • Strong-coupling effect
  • Ultracold Fermi gas

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Materials Science(all)
  • Condensed Matter Physics


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