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

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...

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Bibliographic Details
Published in:Journal of low temperature physics 2017-06, Vol.187 (5-6), p.692-698
Main Authors: Kagamihara, D., Ohashi, Y.
Format: Article
Language:English
Subjects:
Characterization and Evaluation of Materials
Condensed Matter Physics
Coupling
Fluids
Low temperature physics
Magnetic Materials
Magnetism
Phase transitions
Physics
Physics and Astronomy
Shear viscosity
Superfluidity
Transition temperature
Viscosity
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Summary: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 T c , 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 π k B , on the BEC side.
ISSN:0022-2291
1573-7357
DOI:10.1007/s10909-017-1770-6