Berlin 2018 – scientific programme
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MA: Fachverband Magnetismus
MA 37: Multiferroic Oxide Thin Films and Heterostructures II (joint session KFM/TT/MA)
MA 37.8: Talk
Wednesday, March 14, 2018, 17:30–17:45, EMH 225
Octahedral tilting, phonons and Goldstone modes in 111-strained perovskites — Magnus Moreau1, Astrid Marthinsen1, Sinead Majella Griffin2, Tor Grande1, Thomas Tybell1, and •Sverre Magnus Selbach1 — 1NTNU Norwegian University of Science and Technology, Trondheim, Norway — 2Lawrence Berkeley National Laboratory, Berkeley, California, USA
Epitaxial strain has been extensively explored to enhance existing and enable new functional properties in perovskites oxide thin films, with the majority of the work done on 001-oriented films. Recent advances in film growth has made other epitaxial orientations possible, and particularly 111-oriented films show interesting properties because of the different symmetry and chemical bonding at the terminating (111) facet. We use density functional theory (DFT) calculations to study the different response to 111- and 001-strain of the octahedral tilt system and the crystal field splitting of perovskite oxides. Unlike 001-strain, 111-strain is parallel to the edges of the oxygen octahedra, and tensile 111-strain can emulate negative hydrostatic pressure, which is not easily realised experimentally for bulk materials. General trends for how 111-strain affects polar and rotational modes are outlined based on calculations of twenty common perovskites. Furthermore, we show that in SrMnO3 compressive 111-strain give rise to Goldstone-like phonon modes with a Mexican hat-shaped energy surface, while large tensile strain can induce polar Goldstone modes. The chemical and structural requirements for engineering structural Goldstone modes in 111-strained perovskites are finally discussed.