Signatures of polaronic excitations in quasi-one-dimensional ${\mathrm{LaTiO}}_{3.41}$

The optical properties of quasi-one-dimensional metallic ${\mathrm{LaTiO}}_{3.41}$ are studied for the polarization along the a and b axes. With decreasing temperature modes appear along both directions suggestive for a phase transition. The broadness of these modes along the conducting axis might be due to the coupling of the phonons to low-energy electronic excitations across an energy gap. We observe a pronounced midinfrared band with a temperature dependence consistent with (interacting) polaron models. The polaronic picture is corroborated by the presence of strong electron-phonon coupling and the temperature dependence of the dc conductivity.