A Raman study of the charge-density-wave state in A_0.3MoO₃(A = K, Rb)

Abstract

We report a comparative Raman spectroscopic study of the quasione-dimensional
\ncharge-density-wave (CDW) systems A0.3MoO3 (A = K,Rb).
\nTemperature- and polarization-dependent experiments reveal charge-coupled
\nvibrational Raman features. The strongly temperature-dependent collective
\namplitudon modes in the two materials differ by about 3 cm−1
\n, thus revealing
\nthe role of the alkali atom. We discuss the observed vibrational features in terms
\nof the CDW ground state accompanied by a change in the crystal symmetry. A
\nfrequency-kink in some modes seen in K0.3MoO3 between T = 80 and 100 K
\nsupports the first-order lock-in transition, unlike the case of Rb0.3MoO3. The
\nunusually sharp Raman lines (limited by the instrumental response) at very
\nlow temperatures and their temperature evolution suggests that the decay of the
\nlow-energy phonons is strongly influenced by the presence of the temperaturedependent
\nCDW gap