Impurity Effects on Quantum Depinning of Commensurate Charge Density   Waves
  We investigate quantum depinning of the one-dimensional (1D) commensurate charge-density wave (CDW) in the presence of one impurity theoretically. Quantum tunneling rate below but close to the threshold field is calculated at absolute zero temperature by use of the phase Hamiltonian within the WKB approximation. We show that the impurity can induce localized fluctuation and enhance the quantum depinning. The electric field dependence of the tunneling rate in the presence of the impurity is different from that in its absence. 
Masanori Yumoto, Hidetoshi Fukuyama, Hiroshi Matsukawa and Naoto   Nagaosa