Optimal heat transport in rotating Rayleigh-Bénard convection at large Rayleigh numbers

Moderate rotation is able to enhance the heat transport in (rotating) Rayleigh-B\'enard convection. While the heat transport can significantly exceed the nonrotating value for Rayleigh numbers R0{0ex}a510^8, no or only little enhancement remains at larger R0{0ex}a. Here, we aim to identify the reason for the vanishing heat transport enhancement and its different behavior towards large R0{0ex}a: How is the loss of enhancement related to the onset of geostrophic turbulence? What role does rotation-induced shearing at the plates play in this context?