Abstract
A strong Kohn anomaly in is identified in the mostly transverse acoustic phonon branch along the modulation vector with polarization along the direction. This soft mode freezes to zero frequency at the transition temperature , and the temperature dependence of the frequency is strongly affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate superstructure shows a power-law scaling of the intensity and the correlation length that is compatible with an order parameter of dimension .
- Received 28 November 2008
DOI:https://doi.org/10.1103/PhysRevLett.102.086402
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