Raman inactive phonon-polariton dispersion in quantum paraelectric SrTiO₃ crystals studied by FTIR

ABSTRACT

The dispersion relation of Raman inactive phonon-polaritons with T_1u symmetry was studied in quantum paraelectric SrTiO₃ with centrosymmetric Pm3¯m in which no Raman active mode is allowed. The reflectivity in the far- and mid-IR regions was measured using a [001] crystal plate by the reflection FT-IR spectroscopy, and the complex refractive index was determined in the broadband frequency range between 30 and 1200 cm⁻¹. Using these values the dispersion relation of phonon-polariton frequency was discussed using the real and imaginary parts of a polariton wave vector considering the spacial decay of polariton.

KEYWORDS:

• SrTiO₃
• FTIR
• phonon-polariton
• Raman inactive