Shear viscosity of a universal Fermi gas near the superfluid phase transition

Understand

We precisely measure the shear viscosity for a resonantly interacting Fermi gas as a function of temperature, from nearly the ground state through the superfluid phase transition at a critical temperature $T_c$.

• Using an iterative method to invert the data, we extract the {\it local} shear viscosity coefficient $\alpha_S(\theta)$ versus reduced temperature $\theta$, revealing previously hidden features.
• We find that $\alpha_S$ begins to decrease rapidly with decreasing $\theta$ well above $T_c$, suggesting that preformed pairs play an important role.
• Further, we observe that the derivative $\alpha_S'(\theta)$ has a maximum at $T_c$.