Abrupt orthorhombic relaxation in compressively strained ultrathin <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>SrRu</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> films
Prahald Siwakoti, Zhen Wang, Mohammad Saghayezhian, David Howe, Zeeshan Ali, Yimei Zhu, Jiandi Zhang
Abstract
Lattice structure can dictate electronic and magnetic properties of a material. Especially, reconstruction at a surface or heterointerface can create properties that are fundamentally different from those of the corresponding bulk material. We have investigated the lattice structure on the surface and in the thin films of epitaxial $\mathrm{SrRu}{\mathrm{O}}_{3}$ with the film thickness up to 22 pseudocubic unit cells (u.c.), using the combination of surface sensitive low energy electron diffraction and bulk sensitive scanning transmission electron microscopy. Our analysis indicates that, in contrast to many perovskite oxides, the $\mathrm{Ru}{\mathrm{O}}_{6}$ tilt and rotational distortions appear even in single unit cell $\mathrm{SrRu}{\mathrm{O}}_{3}$ thin films on cubic $\mathrm{SrTi}{\mathrm{O}}_{3}$, while the full relaxation to the bulklike orthorhombic structures takes 3--4 u.c. from the interface for thicker films. Yet the $\mathrm{Ti}{\mathrm{O}}_{6}$ octahedra of the substrate near the interface with $\mathrm{SrRu}{\mathrm{O}}_{3}$ films show no sign of distortion, unlike those near the interface with $\mathrm{CaRu}{\mathrm{O}}_{3}$ films. Two orthogonal in-plane rotated structural domains are identified. These octahedral distortions are essential for the understanding of the thickness dependent transport and magnetism in ultrathin films.