Charge Density Wave Transitions in NbS₃ Whiskers
K. Praveena1*, Woei Wu Pai2, Hsiang-Lin Liu1
1Department of Physics, National Taiwan Normal University, Taipei-11677, Taiwan
2Center for Condensed Matter Sciences, National Taiwan University, Taipei-10617, Taiwan
* presenting author:Praveena Kuruva, email:praveena@ntnu.edu.tw
Transition metal trichalcogenides (TMD’s) MQ₃ (M = Ti, Zr, Hf, Nb, Ta; Q = S, Se) have attracted much attention in the physics community because of their unusual properties including superconductivity, Peierls instability, and charge density wave (CDW) transitions. NbS₃, phase II, is standing out for its extremely high Peierls transition temperature, TP = 330–355 K. In this work, we present a Raman scattering study of NbS₃ (phase II) whiskers over a wide temperature range (10 K ~ 450 K). The room temperature Raman phonon modes were assigned as follows: A low-frequency peak at 151 cm-¹ is caused by lattice compression along the columns (T'y mode), and the one at 159 cm-¹ is a Nb–Nb stretching mode. The prominent peak at 193 cm-¹ may be assigned to Nb–(S₂)²- vibrations. Symmetrical valence Nb–S vibrations appear at 260 cm-¹. Weak peaks in the frequency of 298–319 cm-¹ may be ascribed to the Nb–S²- intrachain vibrations, and the peaks at 375 cm-¹ and 387 cm-¹ originate from Nb–S²- interchain modes. The high-frequency bands at 556–568 cm-¹ are due to stretching vibrations of S–S bonds in (S²)²- pairs. The transport properties reveal that it has transitions at TP₁ = 365 K and TP₂=150 K. CDW1 is stable and not so sensitive to growth conditions. CDW2 strongly depends on growth conditions. Nevertheless, it also shows sliding and synchronization. At TP₁, a discontinuous change in the frequency of the 159 cm-¹ and 193 cm-¹ modes was observed.


Keywords: Transition Metal Dichalcogenides, Charge density wave, Raman scattering spectroscopy.