Speakers: Serge Nakhmanson (Argonne National Laboratory)
Place: Na Slovance, přednáškový sál v přízemí
Presented in English
Organisers:
Department of Dielectrics
Multifunctional ferroic materials whose polarization, magnetization and strain could be controlled by an external influence, e.g., stress or electric/magnetic field, are a hallmark of modern engineering and technology. Both “hard” (complex oxides) and “soft” (polymers), they display a vast range of interesting physical phenomena that are yet to be fully understood and can lead to new and unusual functionalities. Showcasing one of such unexpected phenomena, with the help of first-principles-based computational techniques, we predict that Goldstone-like states (i.e., collective, close to zero frequency excitations of the system, requiring practically no consumption of energy) can be artificially induced in a layered-oxide compound with polarization constrained to a plane. Such excitations had been shown to exist in ferroelectric liquid crystals, which have very weak polarization, and some magnetic structures (as spin waves) but never before in “hard” polar materials. We demonstrate that in the layered-oxide system their presence results in an emergence of a variety of highly useful physical properties that include large, tunable dielectric constants and an ability to easily form vortex polar states in a nanodot geometry. In a similar fashion to the well-known perovskite materials with morphotropic phase boundaries (MPBs), these states emerge as polarization rotations with almost no energy penalty, suggesting that the existence of an MPB is actually yet another manifestation of the Goldstone theorem in solids. Unique functionalities of the proposed template compound with Goldstone-like behavior can be exploited for improved energy generation, storage and conversion, opening up new avenues for disruptive advances in electroactive materials design.
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