Competition between shear melting and Taylor instabilities in colloidal crystals

We study the onset of the Taylor instability for colloidal crystals in a narrow-gap Couette Cell. There is a natural competition between the radial flow required for Taylor rolls and the resistance to such motion caused by the anisotropy of the flowing solid. A new, combined Taylor shear-melting instability is found at rotation rates above those expected for the formation of rolls, but below the shear rate required for shear melting in the absence of the Taylor instability. The control parameter for the shear melting transition appears to be a critical shear stress rather than the shear rate.