Anomalous minimum in the shear viscosity of a Fermi gas

Understand

We measure the static shear viscosity $\eta$ in a two-component Fermi gas near a broad collisional (Feshbach) resonance, as a function of interaction strength and energy.

• We find that $\eta$ has both a quadratic and a linear dependence on the interaction strength $1/({k_{FI}a})$, where $a$ is the s-wave scattering length and $k_{FI}$ is the Fermi wave vector for an ideal gas at the trap center.
• For energies above the superfluid transition, the minimum in $\eta$ as a function of interaction strength is significantly shifted toward the BEC side of resonance, to $1/(k_{FI}a)\simeq 0.25$.