Influence of irradiation defects on charge‐density‐wave systems

The consequences of controlled irradiation-induced disorder have been examined in experiments carried out on several low-dimensional conductors that show charge-density wave phenomena. The most prominent action of the irradiation-induced defects is the pinning of the charge-density-wave. It is effective at concentrations starting from the ppm level as evidenced by the effect on the threshold of the collective (sliding mode) conductivity. At higher concentrations the defects start to influence the stability of the charge-density-waves and simultaneously the effect on the structural coherence of incommensurate or commensurate charge-density-wave phases becomes evident in the diffraction and electron microscope studies on irradiated samples. Defects perturb strongly the usual normal metal-incommensurate-commensurate charge-density-wave transition sequence in spite of the fact that they do not suppress completely the instability towards the condensed charge-density-wave phase. The existence of metastable pinned configurations and memory effects in association with defects has also been clearly demonstrated.