Polarization fluctuations in pure SrTiO3

The dielectric susceptibility of pure strontium titanate (ST) was measured as a function of temperature in the range from 4 to 140 K. The analysis of the data obtained has shown that the Barrett formula cannot well reproduce the experimental data. In order to elucidate the nature of this discrepancy we have computed the electric zero-field susceptibility in the framework o f the interacting anharmonic quantum oscillator model. A perturbation theor y technique was employed. We show that the susceptibility obtained in the f ourth order of the theory can nicely reproduce the experimental data. Hence , a reason for the unusual low-T behavior of the electric susceptibility in ST is the existence of large quantum fluctuations at low T.