E138 Forschung

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Oxide heterostructures

Complex oxide compounds display a broad spectrum of properties, including multiferroicity, superconductivity and colossal magnetoresistance. The complex interactions between the electronic, orbital, spin and lattice degrees of freedom result in many phases very close in energy and highly tuneable by external parameters such as temperature, magnetic field or strain.

Many complex oxides crystallize in the perovskite structure (see Figure), or a closely related one. The perovskite chemical formula is ABO3, where A and B are two cations, and O is an oxygen anion. Structural distortions of the ideal cubic perovskite structure often occur to accommodate different elements with a variety of phases and valence states. Rotations and tilts of the oxygen-octahedra BO6 units are the most common distortions. In addition to the perovskite structure, we also investigate double-perovskite (A2BB’O6) and Ruddlesden-Popper (i.e. A2BO4) phases.

By stacking layers of perovskite-like oxide compounds one on top of another, we can further manipulate and tune the bulk properties of oxides and even access new phases not displayed in the parent compounds. The numerous structural and electronic reconstructions are at the heart of this success. Dimensionality effects can also be investigated. The simplest heterostructure is a thin film, in which one compound is grown on a substrate. When multiple layers are repeatedly stacked one on the other, generating artificial layered materials, one speaks about superlattices (see Figure). Understanding the structure-property relationship is key for the design of materials with desired functionalities.

We grow the oxide heterostructures by RHEED-equipped off-axis magnetron sputtering.

Contact: M. Gibert

Contact - Theory: K. Held

Oxide heterostructures

Perovskite structure of a complex oxide

Schematic representation of a perovskite structure (left) and a perovskite-based thin film (middle) and superlattice (right)