Effect of pressure on the polarized infrared optical response of quasi-one-dimensional LaTiO_(3.41)

The pressure-induced changes in the optical properties of the quasi-one-dimensional conductor LaTiO$_{3.41}$ were studied by polarization-dependent mid-infrared micro-spectroscopy at room temperature. For the polarization of the incident radiation parallel to the conducting direction, the optical conductivity spectrum shows a pronounced mid-infrared absorption band, exhibiting a shift to lower frequencies and an increase in oscillator strength with increasing pressure. On the basis of its pressure dependence, interpretations of the band in terms of electronic transitions and polaronic excitations are discussed. Discontinuous changes in the optical response near 15 GPa are in agreement with a recently reported pressure-induced structural phase transition and indicate the onset of a dimensional crossover in this highly anisotropic system.