Fig. 2: Shear viscosity spectral function and anomalous damping of the quadrupole mode.
From: Odd-parity effect and scale-dependent viscosity in atomic quantum gases
a Shear viscosity spectral function in units of ℏn, where n is the particle density at the center of the harmonic trap, as a function of wave number q and frequency ω (both in thermal units with \({\lambda }_{T}=\sqrt{2\pi \beta {\hslash }^{2}/{m}^{* }}\)). The white solid (dashed) line describes the path in parameter space (q = 1/R, ω = ωQ) explored by tuning the trap confinement for N1 = 103 (N2 = 106) atoms. b–d Ratio of the shear viscosity spectral function η(ω = ωQ, q = 1/R) and the hydrodynamic shear viscosity ηHD = η(ωQ, 0) as a function of b trap frequency, c interaction strength, and d particle number. Unless otherwise specified, we use an atom number N = 103 and interaction strength \(\ln ({k}_{F}{a}_{2})=0.63\) (corresponding to βμ = 9). In each case, we observe a pronounced deviation from the hydrodynamic prediction for smaller atom number, interactions that are deeper in the BCS limit, and for weaker harmonic traps (or lower temperatures), respectively.
