Effects of tungsten doping on the CDW states of η-Mo₄O₁₁

The η-Mo₄O₁₁ system shows successive CDW transitions due to its two-dimensional Fermi surface instability. We find that the lower temperature CDW-II transition easily disappears by doping a small amount of W atoms (less than 0.2%/Mo), though the higher temperature CDW-I transition is weakly depressed. The W atoms possibly substitute both the intra- and the inter-layer Mo sites. The doping effectively reduce the carrier compensation, leading to the suppression of T_CDW-I. Moreover, the interlayer coherence between the intralayer two-dimensional CDWs may be destroyed by the substitution between the layers since the modulation of CDW-II state has an interlayer component. The resistivity along the conducting plane follows "logT" dependence below 10 K, suggesting that the W atoms doped within the layer should induce the Anderson-type charge localization.