THEORY OF IMPURITY-INDUCED LATTICE-DISTORTIONS IN THE NORMAL-PHASE OFCHARGE-DENSITY-WAVE SYSTEMS

A phenomenological Ginzburg-Landau theory is applied to the normal pha se of one-dimensional charge-density-wave systems with a finite concen tration of impurities. It is found that the interaction between the im purities and the highly polarizable electron gas leads to a strong and oscillatory impurity-impurity interaction, which in turn leads to ord ered impurity arrangements and to sizable periodic lattice distortions . The effect is very strongly dependent on the charge of the impuritie s, their concentration, and their (interstitial) location in the latti ce unit cell. All these factors modify drastically. the periodicity as sociated with the lattice distortion. The theory explains satisfactori ly the changing modulation recently observed by atomic-force microscop y in the normal (room-temperature) phase of NbSe3 with a variety of im purities.