Interaction between Charge Density Waves in the Monoclinic Phase of NbS3

In the monoclinic polytype NbS 3 -II, the monoclinic b -axis of which coincides with the direction of greatest conductivity, two charge density waves (CDWs) have been observed at room temperature: CDW-0 with the wave vector q 0 = 0.5 a * + 0.352 b * + 0.5 c * and CDW-1 with the wave vector q 1 = 0.5 a * + 0.298 b * + 0.5 c *. X‑ray diffraction patterns obtained in the temperature range of 90–500 K have shown that the vectors q 0 and q 1 depend on the temperature, but their b * coordinates satisfy the relation $$2q_{0}^{{{\mathbf{b}}\text{*}}}(T) + q_{1}^{{{\mathbf{b}}\text{*}}}(T) = {\text{const}} = 1$$ . It has been concluded that the wave vector q 1 of CDW-1 is determined not only by the nesting of Fermi surfaces, but also by the vector q 0 , because CDW-1 is adjusted to the second harmonic of CDW-0, which indicates the interaction between charge density waves. This conclusion has been confirmed by structural studies of NbS 3 -II samples, the lattice of which is strongly deformed due to a high concentration of twins. In these samples, CDW-0 is conserved, and the wave vector of CDW-1 has the b * component not related to q 0 .