Optical detection of symmetry breaking on a nanoscale in SrTiO₃:Ca

Abstract

Abstract Spontaneous and field-induced linear birefringence is measured at low temperatures on single-domained single crystals of weakly doped SrTiO3:Ca (x = 0·002 and 0·007) in order to investigate polar ordering processes near to Tc ≈ 4 and 18 K, respectively. In agreement with direct polarization measurements the size of mesoscopic polar nanodomains is determined within the framework of a nonlinear polarization optical response model. Quasi-first-order Raman scattering of soft and hard polar modes, TO1, TO2 and TO4, is observed on local precursor nanodomains above Tc . Below Tc the change of the global symmetry from D4h to C2v is reflected by selection rules imposed on first-order Raman lines in various scattering geometries.