Measurement of soft mode damping in SrTiO 3 by FIR surface waves

Abstract

The results of investigation of low-frequency modes in SrTiO 3 crystals by FIR surface electromagnetic waves (SEW) are presented. Amplitude and phase spectroscopy methods, including SEW heterodying for the complex SEW refraction index n ef measurements at temperatures of 80–300 K were applied. The SEW method appears to be convenient for the soft mode (SM) frequency and damping measurements and advantages against other method are discussed. The possible reasons of disagreement of SEW damping values at v = 84 cm −1 obtained by us and others are discussed. Sharp increase of SEW damping at this frequency when temperature increases was explained by transition of Fano type mode ( v < v TO) to Zenneck-Sommerfeld one ( v > v TO) with sufficiently larger damping. At liquid N temperature SM frequency take the value of 43 cm −1. It sufficiently well agrees with the one obtained by hyper-Raman and IRR methods. YBa 2Cu 3O 7 − x thin films Preliminary experiments with ferroelectric Ba x Sr 1 − x TiO 3 and superconducting on SrTiO 3 showed the SEW sensitivity to the phase transitions of films. The maximum of SEW damping in Ba x Sr 1 − x TiO 3 at the phase transition temperature was obtained. The plasma frequency v p as well as electron collisional frequency v τ in YBa 2Cu 3O 7 − x was obtained ( v p = 10 4cm −1, v t = 3000 cm −1 at 300 K).