Critical behavior and multistability in quasi-two-dimensional turbulence

Turbulence in two dimensions tends to order the flow into large-scale vortices via the inverse cascade. In between 2D and 3D, quasi-2D flows show rich behavior: both the direction of the turbulent cascade and the large-scale condensation of turbulent energy display critical behavior in the dependence on flow parameters. In this work, we experimentally study the transition to turbulence in quasi-2D nanofluidic channels using superfluid helium. We find a cascade of metastable coexisting states (pictured is the large-scale dissipation as a function of flow velocity), whose exact origin remains uncertain. The transitions between states follow scaling of certain nonequilibrium phase transitions.