Features of a Low-Temperature Charge Density Wave in the Monoclinic Phase of NbS3 Manifested in the NMR and in Transport Properties

The relaxation of the transverse nuclear magnetization in the monoclinic phase of NbS 3 has been studied by the 93 Nb nuclear magnetic resonance method near the temperature T P2 = 150 K, at which a low-temperature charge density wave is formed. It has been shown that the critical slowing down of one of the vibrational modes of the lattice, which is quite slow even above T P2 , occurs slightly below T P2 . The transition at T P2 occurs not only in low-resistance samples, as thought previously, but also in high-resistance ones, and involves Nb atoms in the bulk of a sample. The transport properties of high-resistance samples, namely, the smearing of the depinning threshold for the charge density wave below T P2 , confirm that the phase transition in them occurs at T P2 . It has been concluded that the distortion of the lattice at T P2 is not due to the Peierls mechanism and can be attributed to the Keldysh–Kopaev transition. Another possible mechanism is the fluctuation distortion of the lattice above T P2 that prevents the sliding of the charge density wave.