Ratio of shear viscosity to entropy density in multifragmentation of Au + Au

The ratio of the shear viscosity ($\eta$) to entropy density ($s$) for the intermediate energy heavy-ion collisions has been calculated by using the Green-Kubo method in the framework of the quantum molecular dynamics model. The theoretical curve of $\eta \mathrm{/}s$ as a function of the incident energy for the head-on Au+Au collisions displays that a minimum region of $\eta \mathrm{/}s$ has been approached at higher incident energies, where the minimum $\eta \mathrm{/}s$ value is about 7 times Kovtun-Son- Starinets (KSS) bound (1/4$\pi$). We argue that the onset of minimum $\eta \mathrm{/}s$ region at higher incident energies corresponds to the nuclear liquid gas phase transition in nuclear multifragmentation.