Discontinuous Thinning in Active Microrheology of Soft Complex Matter
  Employing theory and numerical simulations, we demonstrate discontinuous force thinning due to the motion of an external probe in a host medium, which we approximate as structureless. When the driving of the probe exceeds a critical force, the microviscosity of the medium drops abruptly by about an order of magnitude. This phenomenon occurs for strong attractive interactions between probe and a sufficiently dense host medium. 
R. Wulfert and U. Seifert and T. Speck
cond-mat.soft