Berlin 2015 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 4: Focused Session on Ferroic Domain Walls I (DF with MA)

DF 4.4: Topical Talk

Montag, 16. März 2015, 16:10–16:40, EB 107

Field-induced hysteresis of chiral vortices in ferroelectric SrTiO₃ twin walls. — •Ekhard Salje — University of Cambridge, Cambridge, UK

Resonant piezoelectric spectroscopy shows polar resonances in paraelectric SrTiO₃ at temperatures below 80 K. These resonances become strong at T < 40 K. This piezoelectric response does not exist in paraelastic SrTiO₃ nor at temperatures just below the ferroelastic phase transition. The interpretation of the resonances is related to ferroelastic twin walls which become polar at low temperatures in close analogy with the known behavior of CaTiO₃. SrTiO₃ is different from CaTiO₃, however, because the wall polarity is thermally induced; i.e., there exists a small temperature range well below the ferroelastic transition point at 105 K where polarity appears on cooling. As the walls are atomistically thin, this transition has the hallmarks of a two-dimensional phase transition restrained to the twin boundaries rather than a classic bulk phase transition. Simulations of polar twin walls in SrTiO₃ show nanoscopic vortices, which can be switched in orientation under an external electric field. The hysteresis of the vortex polarization inside the twin boundary leads to direct applications in non-volatile memory devices. E.K.H. Salje et al. Domains within Domains and Walls within Walls: Evidence for Polar Domains in Cryogenic SrTiO₃, Phys. Rev. Lett. 111, 24, 247603 (2014), Zykova-Timan T and Salje E.K.H. Highly mobile vortex structures inside polar twin boundaries in SrTiO3, APL 104, 082907 (2014).