Phase transitions and soft modes in ferroelectric superlattices
- 18 June 1990
- journal article
- Published by IOP Publishing in Journal of Physics: Condensed Matter
- Vol. 2 (24) , 5409-5431
- https://doi.org/10.1088/0953-8984/2/24/013
Abstract
A theory of periodic ferroelectric multilayers is presented. The multilayer system consists of two alternating ferroelectrics with different transition temperatures. The system is described by a Ginzburg-Landau functional with space-dependent coefficients. In particular, the authors consider the case of a ferroelectric phase transition of first order. Expressions for static properties such as transition temperature, supercooling temperature and polarisation profile are derived. Immediately below the transition temperature there are unpolarised domains within the stronger ferroelectric layers. Their existence is due to the possible phase coexistence of the ordered and disordered phases in the corresponding bulk material. In order to describe the soft-mode dynamics they use phenomenological equations of motion and study the spectrum of transverse optical modes. The lowest bands are almost dispersion-free and the corresponding modes are confined to those layers which have the lower bulk soft-mode frequency. Because the bulk soft modes of the two layers soften at different temperatures the localisation of the modes in one or the other layer depends upon the temperature. This temperature dependence of the mode form can be seen in the lineshape of the polarisation correlation function if the soft-mode damping of the two layers is different. Furthermore, interface modes are shown to exist. Their energy lies below the continuum, confined by the two bulk soft-mode frequencies. These modes result from the special form of the inhomogeneous polarisation profile in a superlattice in contrast to the Fuchs-Kliever interface modes, which have their origin in the long-range dipolar interaction. The number of these bound states depends on the temperature.Keywords
This publication has 20 references indexed in Scilit:
- Ferromagnetic multilayers: Statics and dynamicsPhysical Review B, 1988
- Coupled-mode stop bands of acoustic phonons in semiconductor superlatticesPhysical Review B, 1987
- Superlattices of IV-VI CompoundsPhysica Scripta, 1987
- Space-charge layers in semi-insulating GaAs: Photoexcited two-dimensional electron systemsSuperlattices and Microstructures, 1985
- Electronic structure ofTe superlatticesPhysical Review B, 1984
- Semi-infinite systems with first-order bulk transitionsPhysical Review B, 1983
- Ginzburg-Landau theory of static domain walls in shape-memory alloysZeitschrift für Physik B Condensed Matter, 1983
- Temperature dependence of macroscopic quadrupole moment near phase transition pointsFerroelectrics, 1981
- Interaction of Elastic Strain with the Structural Transition of Strontium TitanatePhysical Review B, 1970
- Conduction Electrons and Optic Modes of Ionic CrystalsPhysical Review Letters, 1965