Inelastic neutron scattering is used to measure the temperature dependent phonon dispersion in Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ ($x=0.4$, 0.6). The in-plane $Sigma_{4}$ octahedral tilt mode softens significantly at the zone boundary of the high temperatur
e tetragonal (HTT) textit{I4}$_{mathit{1}}$textit{/acd} structure as the temperature approaches the transition to a low temperature orthorhombic (LTO) textit{Pbca} phase. This behavior is similar to that in La$_2$CuO$_4$, but a new inelastic feature that is not found in the cuprate is present. An anomalous phonon mode is observed at energy transfers greater than the $Sigma_{4}$ albeit with similar dispersion. This anomalous phonon mode never softens below $sim 5$ meV, even for temperatures below the HTT-LTO transition. This mode is attributed to the presence of intrinsic structural disorder within the textit{I4}$_{mathit{1}}$textit{/acd} tetragonal structure of the doped ruthenate.
The Fermi surface (FS) of ErTe3 is investigated using angle-resolved photoemission spectroscopy (ARPES). Low temperature measurements reveal two incommensurate charge density wave (CDW) gaps created by perpendicular FS nesting vectors. A large Delta_
1 = 175 meV gap arising from a CDW with c* - q_CDW1 ~ 0.70(0) c* is in good agreement with the expected value. A second, smaller Delta_2 = 50 meV gap is due to a second CDW with a* - q_CDW2 ~ 0.68(5) a*. The temperature dependence of the FS, the two gaps and possible interaction between the CDWs are examined.
