Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance Study of181Ta in the Commensurate Charge Density Wave State of 1T-TaS2

The nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) of the 181 Ta nuclei have been made on 1 T -TaS 2 at 4.2 K in order to get detailed information on the superlattice structure in the commensurate charge density wave state of this material from a microscopic viewpoint. The NMR ane NQR spectra are consistent with the star-shaped cluster model inferred from diffraction experiments. Furthermore the spectra indicate that the commensurate phase of 1 T -TaS 2 has a complicated and somewhat disordered stacking of CDW layers in contrast with that of isostructural 1 T -TaSe 2 (the ordered \({c}₀+{2a}₀\) stacking). On the basis of these results, we propose a new picture of the semiconductive origin of 1 T -TaS 2 , including an explanation of the quite different behaviors of the low temperature conduction between 1 T -TaS 2 and 1 T -TaSe 2 .