Self Organized Nano-Structures in SrTiO₃ Induced by Plastic Deformation

Plastic deformation of SrTiO₃ single crystals is known to generate a superstructure of line dislocations as confirmed by X-ray and neutron diffraction¹. Enhancement of superconductivity and anisotropic conductivity was hypothesized to occur along these dislocation structures. Local strain is known to shift the energy and dissipation of phonons, with strong implications for the mid-infrared optical response in polar crystals. A Scanning Near-field Optical Microscope equipped with a balanced asymmetric Michelson interferometer imaged nanoscale variations in the optical phonon response in plastically deformed SrTiO3. Phase-resolved nano-spectroscopy performed near walls of line dislocations was used to infer the optical phonon parameters and quantify dislocation-induced strain fields in the crystal.

The optical phonon response exhibits a periodic texture of lines correlated with nano-scale surface corrugation oriented perpendicular to the strained axis. Shifts in the surface potential measured using Kelvin probe force microscopy correlate with these dislocation structures, and provides evidence for local strain-induced ferroelectric order. This represents a novel approach to directly probe the real-space superstructure of plastically deformed superconducting ceramic oxides.

[1] Hameed et al. Nat. Mater. 21, 54-61 (2022)