Abstract
We report a comparative Raman spectroscopic study of the quasi-one-dimensional charge-density-wave (CDW) systems A0.3MoO3 (A = K, Rb). Temperature- and polarization-dependent experiments reveal charge-coupled vibrational Raman features. The strongly temperature-dependent collective amplitudon modes in the two materials differ by about 3 cm−1, thus revealing the role of the alkali atom. We discuss the observed vibrational features in terms of the CDW ground state accompanied by a change in the crystal symmetry. A frequency-kink in some modes seen in K0.3MoO3 between T = 80 and 100 K supports the first-order lock-in transition, unlike the case of Rb0.3MoO3. The unusually sharp Raman lines (limited by the instrumental response) at very low temperatures and their temperature evolution suggests that the decay of the low-energy phonons is strongly influenced by the presence of the temperature-dependent CDW gap.
Highlights
H3A 2K6, Canada. 5 Present address: Experimentalphysik 2, Universität Augsburg, 86135 Augsburg, Germany. 6 Author to whom any conrrespondence should be addressed
A Raman study of the anomalous profile of the amplitudon mode in K0.3MoO3 was reported [13] in which, for temperatures below 100 K, the amplitudon mode showed an anomalous ‘fin’-like profile toward the Stokes side of its central frequency. This was interpreted as a splitting of the amplitudon mode into two or more closely spaced harmonic oscillator-type modes
The splitting was claimed to be due to a strong perturbation of the CDW by impurity potentials
Summary
A Raman study of the anomalous profile of the amplitudon mode in K0.3MoO3 was reported [13] in which, for temperatures below 100 K, the amplitudon mode showed an anomalous ‘fin’-like profile toward the Stokes side of its central frequency. This was interpreted as a splitting of the amplitudon mode into two or more closely spaced harmonic oscillator-type modes. At very low temperatures where there are practically no thermally excited electrons, the impurity potentials remain unscreened, leading to a spatial variation of the CDW amplitude and a splitting of the amplitudon mode.
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