Fig. 3: Phonon collapse and van der Waals melting.
From: van der Waals driven anharmonic melting of the 3D charge density wave in VSe2
a–d Representative IXS spectra at 110 K and their corresponding fitting. The IXS scan at h=2.25 r.l.u. is presented in logarithmic scale due to the large enhancement of the elastic line. ω1 stands for the soft mode. e Temperature dependence of the energy of the ω1 branch and the anharmonic theoretical frequencies obtained with and without van der Waals corrections. The shaded area defines the CDW region. f Temperature dependence of the linewidth. Inset, squared frequency of the soft mode as a function of the reduced temperature. Lines are guides to the eye. The cyan squares in (e) and (f) (inset) refer to the frequency of the ω1 phonon extrapolated to the CDW temperature, since the large enhancement of the elastic line precludes the extraction of its energy from the fitting analysis. The error bars in the experimental data points in panel (e) and (f) represent the fit uncertainty.
