title: Broken local symmetry in paraelectric BaTiO3 proved by second harmonic generation.
abstract: Precursor dynamics of a cubic to tetragonal ferroelectric phase transition in BaTiO3 is studied by the accurate measurement of the second harmonic generation (SHG) integral intensities. A finite signal holds for the SHG integrated intensity above the ferroelectric Curie temperature T(c)=403  K. Above the Burn's temperature T(d)≈580  K, the power law with the exponent γ=1 shows normal SHG nature originating from the hyper-Raman scattering by dynamical polar excitations, while, below T(d), a SHG signal from polar nanoregions becomes dominant with the larger exponent γ=2. Such a crossover of the power law exponent near T(d) is discussed on the basis of the effective Hamiltonian method and Monte Carlo simulation.
authors.affiliation: Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk, 630090, Russia.
authors.forename: A M
authors.initials: AM
authors.lastname: Pugachev
authors.forename: V I
authors.initials: VI
authors.lastname: Kovalevskii
authors.forename: N V
authors.initials: NV
authors.lastname: Surovtsev
authors.forename: S
authors.initials: S
authors.lastname: Kojima
authors.forename: S A
authors.initials: SA
authors.lastname: Prosandeev
authors.forename: I P
authors.initials: IP
authors.lastname: Raevski
authors.forename: S I
authors.initials: SI
authors.lastname: Raevskaya