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HL: Fachverband Halbleiterphysik

HL 66: Thin Oxides and Oxide Layers II (joint session DS/HL)

HL 66.2: Vortrag

Donnerstag, 19. März 2020, 11:15–11:30, CHE 91

In-situ observation of sub-unit-cell nonlinear polarization in superlattices of layered oxides — •Johanna Nordlander¹, Marco Campanini², Marta D. Rossell², Manfred Fiebig¹, and Morgan Trassin¹ — ¹ETH, Zurich, Switzerland — ²EMPA, Dübendorf, Switzerland

When approaching the 2D-limit of a material, finite size, edge or confinement effects often lead to phenomena that differ from the bulk behavior and promote novel functionalities. In materials with a layered structure, the individual sub-unit-cell layers that form their fundamental building blocks may exhibit a different symmetry, and hence different properties, than those of the parent material. For example, strong nonlinear optical properties may arise from broken inversion symmetry in fractional unit-cells of an otherwise centrosymmetric layered oxide. Here we use in-situ optical second harmonic generation (ISHG) during thin-film deposition to access these unique symmetry properties of sub-unit-cell layers in ultrathin, naturally layered hexagonal manganites. A strong nonlinear polarization directly originating from the inversion-symmetry breaking of individual half-unit-cell layers leads to a striking modulation of ISHG intensity connected to the periodic cancellation and reappearance of a non-centrosymmetric thin-film structure as each half-unit-cell layer is added during thin-film synthesis. We thus reveal the unexpectedly strong optical response of these sub-unit-cell blocks that perfectly cancel in the bulk limit. We furthermore make use of this characteristic dynamic ISHG signature to create oxide superlattices through sub-unit-cell symmetry control.