Mode-Locking Hysteresis in the Globally Coupled Model of Charge-Density Waves

We study the response of a recently proposed global coupling model of charge-density waves to a joint ac+dc drive. The model is the standard Fukuyama-Lee-Rice model with an additional global coupling term to account for interaction with (uncondensed) quasi-particles. We find that traditional mode-locking is accompanied by hysteresis on mode-locked steps. The experimentally observed asymmetry in the size of hysteresis is reproduced and explained by drawing attention to the importance of the pinning force. For large values of global coupling, increased rigidity leads to vanishing of subharmonic steps consistent with experiments.