SrTiO3: Thoroughly Investigated but Still Good for Surprises

For decades, SrTiO3 has been in the focus of research with seemingly never-ending new insights regarding its ground state properties, application potentials, its surface and interface properties, the superconducting state, the twin boundaries, domain functionalities, etc. Here, we focus on the already well-investigated lattice dynamics of STO and show that four different temperature regimes can be identified which dominate the elastic properties, the thermal conductivity, and the birefringence. These regimes are a low-temperature quantum fluctuation-dominated one, followed by an intermediate regime, a region of structural phase transition at similar to 105 K and its vicinity, and at high temperatures, a regime characterized by precursor and saturation effects. They can all be elucidated by lattice dynamical aspects. The relevant temperature dependences of the soft modes are discussed and their relationship to lattice polarizability is emphasized.