Temperature and pressure dependence of the transverse-optic modes of ionic crystals and their associated anharmonic self-energies

Abstract

The temperature dependence (2-300 K) and hydrostatic pressure dependence (0-7 kbar) of the $q\ensuremath{\approx}0$ transverse-optic mode frequency ${\ensuremath{\omega}}_{t}$ and its associated damping $2\ensuremath{\Gamma}(0,t,{\ensuremath{\omega}}_{t})$ are reported for the alkali, silver, and thallium halides. These results are analyzed to yield the temperature dependence of the thermal strain ${\ensuremath{\Delta}}^{E}(0,t)$ and far-infrared anharmonic self-energies ${\ensuremath{\Delta}}_{T}^{A}(0,t,{\ensuremath{\omega}}_{t})$ associated with the mode at ${\ensuremath{\omega}}_{t}$. In addition, calculations of ${\ensuremath{\Delta}}^{E}(0,t)$, ${\ensuremath{\Delta}}_{T}^{A}(0,t,\ensuremath{\Omega})$ at $\ensuremath{\Omega}=0$ and $\ensuremath{\Omega}={\ensuremath{\omega}}_{t}$, and $\ensuremath{\Gamma}(0,t,{\ensuremath{\omega}}_{t})$ are presented for the alkali halides crystallizing in the NaCl structure using current many-body thermodynamic Green's-function anharmonic theories, and these are compared with the experimental results.