Fyzikální ústav Akademie věd ČR

Theoretically predicted ferroelectric phase induced by tensile stress was confirmed in SrTiO₃ epitaxial films and SrTiO₃/DyScO₃ heterostructures on DyScO₃ substrates, prepared in top world laboratories. It is driven near 270 K by a soft phonon mode in the THz range which in the whole measured temperature region of 20-300 K couples to an overdamped excitation of order-of-magnitude lower frequency (obviously of strong anharmonic origin) and is tunable by electric field. This results in a tunable permittivity of such heterostructures up to the THz range, attractive for applications. For details see C. Kadlec et al., J. Phys.: Condens. Matter 21, 115902 (2009), C. Kadlec et al., Phys. Rev. B 80, 174116 (2009) a D. Nuzhnyy et al., Appl. Phys. Lett., in press.

Temperature dependence of polar mode frequencies and high-frequency permittivity in SrTiO₃ thin films on DyScO₃ substrate as evaluated from the IR reflection and THz transmission spectra and from microwave resonance measurements. The film thicknesses are listed in the figure.