Abrupt orthorhombic relaxation in compressively strained ultrathin SrRuO3 films

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 SrRuO3 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 RuO6 tilt and rotational distortions appear even in single unit cell SrRuO3 thin films on cubic SrTiO3, while the full relaxation to the bulklike orthorhombic structures takes 3-4 u.c. from the interface for thicker films. Yet the TiO6 octahedra of the substrate near the interface with SrRuO3 films show no sign of distortion, unlike those near the interface with CaRuO3 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.

Automated summary

The lattice structure of SrRuO3 thin films can differ significantly from that of the corresponding bulk material, with RuO6 distortions appearing even in single unit cell films. Thicker films require 3-4 unit cells to fully relax to a bulklike orthorhombic structure. The TiO6 octahedra of the substrate near the interface with SrRuO3 films remain undistorted, unlike those near CaRuO3 film interfaces.