Nonlinear dielectric susceptibility in SrTiO3 and possible nature of the low-temperature phase

The nonlinear dielectric susceptibility of SrTiO3 is studied experimentally. Intense higher-order harmonics of the polarization, whose amplitudes grow with decreasing temperature and saturate at T less than or equal to 4 K, are observed in the temperature range T<50 K. Hysteresis phenomena, differences in the zero-field cooling (ZFS) and field cooling (FC) regimes for the higher-order harmonics, are observed when a constant electric field is applied. The existence in SrTiO3 of a strongly frustrated state, which arises when the interaction of the structural and ferroelectric order parameters is taken into account, is proposed. The low-temperature state of SrTiO3 is analyzed on die basis of a phase diagram which is similar to that of a spin glass [S. Kirkpatrick and D. Sherington, Phys. Rev. B 17, 4384 (1978); J, R. L. De Almeida and D. J. Thouless, J. Phys. A 11, 983 (1978)]. (C) 1996 American Institute of Physics.