Quantum Creep and Quantum-Creep Transitions in 1D Sine-Gordon Chains.

Discrete sine-Gordon (SG) chains are studied with path-integral molecular dynamics. Chains commensurate with the substrate show the transition from pinning to quantum creep at bead masses slightly larger than in the continuous SG model. Within the creep regime, a field-driven transition from creep to complete depinning is identified. The effects of disorder on the chain's dynamics depend on the potential's roughness exponent H. For example, quantum fluctuations are generally too small to depin the chain if H=1/2, while an H=0 chain can be pinned or unpinned depending on the bead masses. Thermal fluctuations always depin the chain.