The Jahn-Teller distortion (JTD) in ABO3 perovskite compounds is linked to various functional properties as the electronic band gap size and the magnetic order. Among the perovskite oxides, the rare-earth manganite series R3+Mn3+O3 exhibits one of the largest amplitudes of JTD. In these compounds, the JTD is responsible for opening a band gap, which's size gradually decreases with increasing temperature and eventually disappears together with the JTD ( at ~ 750 K for LaMnO3). Our aim is to design materials in which the non-polar JTD is tunable by an applied external electric fields in order to control optical properties.
We discuss two approaches vis-a-vis the contradictory problem: Hybrid Improper Ferroelectricity (HIF) and manganite thin films epitaxially grown on piezoelectric substrates. In compounds showing HIF, the appearing polar lattice distortion is slave to two non-polar geometrical distortions expressed in a trilinear term in the Landau expansion of the free energy. The involvement of the JTD in this trilinear term indicates the geometrical allowance of manipulating the JTD amplitude with an electric field. The second concept relies on the idea of tuning the JTD by manipulating the strain state of a manganite thin film through an applied electric field onto a piezoelectric substrate. We show why the second approach is conceptually the most promising and discuss how the electro-optic response can be maximized on the basis of our ab-initio results.