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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 11: Ferroics - Domains and Domain Walls (joint session KFM/MA)

KFM 11.9: Vortrag

Mittwoch, 18. März 2020, 18:00–18:20, TOE 317

Photovoltage from ferroelectric domain walls in BiFeO₃ — •Sabine Körbel^1,2, Stefano Sanvito¹, and Jirka Hlinka² — ¹School of Physics & CRANN, Trinity College Dublin, Ireland — ²Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic

Ferroelectric domain walls are objects capable of creating local electric fields in ferroelectric materials, and therefore in principle allow for a domain-wall driven photovoltaic effect. However, up to now the magnitude of such a domain-wall photovoltage was never measured nor calculated directly: experimentally it is hard to distinguish between domain-wall and bulk photovoltaic effect; first principles calculations used only an indirect approach based on the ionic polarization in the dark state, neglecting the electronic polarization. In order to directly calculate the domain-wall photovoltage in BiFeO₃, we modeled the excitonic charge density upon light irradation from first principles and determined the potential variations at the domain walls and consequently the domain-wall photovoltage. We find indeed that excitons form an electric dipole layer at the domain walls resulting in a domain-wall driven photovoltage, and that the excitonic dipole moment is aligned parallel to the net polarization, not, as previously assumed, antiparallel. By comparing the calculated domain-wall photovoltage to the total photovoltage measured in experiment, we conclude that the domain-wall effects are relatively small and cannot account for the major part of the measured photovoltage. This indicates that bulk effects, not domain-wall effects, dominate the photovoltage in BiFeO₃.