ELECTRIC-FIELD-DEPENDENT DIELECTRIC-CONSTANT AND NONLINEAR SUSCEPTIBILITY IN SRTIO3

SrTiO3 belongs to the class of incipient ferroelectrics in which an el ectrically ordered state is suppressed by quantum fluctuations. To inv estigate the nature of these excitations, we have measured the linear and nonlinear susceptibilities of SrTiO3 as a function of temperature T and field E. The application of large fields E counteracts the fluct uations and forces the system into an ordered state. The (E,T) diagram is presented. The field dependence of the dielectric constant can be well described within an Ising model including quantum tunneling. Mini ma in the third harmonic susceptibility, which is a measure of ferroel ectric correlations, are taken as evidence for the onset of coherent t unneling phenomena near T = 33 K.