Nonlinear resonance in crystals strontium titanate and barium titanate

Abstract

ium titanate and barium titanate are examined. Raman modes of B_2g at 235 cm⁻¹ and E_g at 615cm⁻¹, and A₁(LO) modes at 196 and 474 cm⁻¹ are recorded in the tetragonal phases in crystal SrTiO₃ and the reduced BaTiO₃, respectively. All the four Raman lines are asymmetric cut-off on low-energy sides, manifesting the nonlinear interference with the positive coupling coefficients in these two samples which are well compared with BiSrCaCuO with a positive coupling coefficient and YBaCuO with a negative coupling coefficient. The nonlinear resonance including the signs of the Fano coefficient is discussed to attribute to the anharmonic interaction term in the potential function which distorts the line shapes and provides a radiationless channel for the phonons.