Wystąpienie ustne Dominik Wrana (WCN-Wt)
POLARONS AND FERROELECTRICITY AT ATOMIC SCALE ON OXIDE PEROVSKITE SURFACES
1 Department of Surface and Plasma Science, Charles University, Prague, Czech Republic, Ke Karlovu 2027/3, 12116 Praga, Czech Republic
2 Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10, 1040 Wiedeń, Austria
Although perovskite oxides share many common properties, e.g. ABO3 chemical formula or a high dielectric constant, what makes them so interesting is what distinguishes them. Among them one can find materials with such intriguing electronic properties as colossal magnetoresistance, superconductivity, ferroelectricity or charge ordering. In this talk I would like to focus on understanding the atomic origin of two last, especially appealing towards (photo-)catalytic applications.
In order to showcase those mechanisms two perovskite oxide single crystals were chosen - ferroelectric BaTiO3 and incipient ferroelectric KTaO3. As both are insulating, low temperature ncAFM microscopy, equipped with qPlus sensor, was employed. As it will be presented, electric fields emerging from the same metallic tip can cause permanent crystal distortions or charge ordering, depending on the structure of the perovskite surface.
In order to compensate the polarity, bulk-terminated KTaO3(100) surface develops two alternating domains of KO and TaO2 [1]. Excess electrons injected from the AFM tip form quasiparticles called polarons (charges coupled with lattice distortions) which can be further shaped into 1D or 2D structures by emerging electric fields.
Different mechanism applies for the case of BaTiO3(100), a model ferroelectric perovskite. When cooled down to 4K it adopts a rhombohedral crystal structure, where titanium atoms can easily break a symmetry causing a spontaneous polarization. I will present that a biased tip placed a few nanometers above the surface allows for reversible manipulation of individual atoms on the surface, writing and erasing polarized ferroelectric domains.
[1] Setvin, Martin, et al. "Polarity compensation mechanisms on the perovskite surface KTaO3 (001)." Science 359.6375 (2018): 572-575.