Rössle, Matthias Wang, Chen Nan Marsik, Premysl Yazdi-Rizi, M. Kim, Kyung Wan Dubroka, Adam Marozau, Ivan Schneider, C. W. Humlíček, J. Baeriswyl, Dionys Bernhard, Christian 2013-09-26 We have measured the temperature dependence of the direct band gap <i>E</i>_<i>g</i> in SrTiO₃ and BaTiO₃ and related materials with quantum-paraelectric and ferroelectric properties using optical spectroscopy. We show that <i>E</i>_<i>g</i> exhibits an anomalous temperature dependence with pronounced changes in the vicinity of the ferroelectric transition that can be accounted for in terms of the Fröhlich electron-phonon interaction with an optical phonon mode, the so-called soft mode. In addition, we demonstrate that these characteristic changes of <i>E</i>_<i>g</i> can be readily detected even in very thin films of SrTiO₃ with a strain-induced ferroelectric order. Optical spectroscopy thus can be used as a rather sensitive probe of ferroelectric order in very thin films of these titanates and probably also in subsequent multilayers and devices. application/pdf https://folia.unifr.ch/global/documents/303259 https://folia.unifr.ch/documents/303259/files/ber_opf.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevB.88.104110 info:eu-repo/semantics/openAccess License undefined Physical Review B. - 2013, vol. 88, no. 10, p. 104110 info:eu-repo/classification/udc/53 Optical probe of ferroelectric order in bulk and thin-film perovskite titanates http://purl.org/coar/resource_type/c_6501