Nano-resolved insulator-metal domain textures in a polar bilayer ruthenate

The 4d transition metal oxides of the Ca_n+1Ru_nO_3n+1 perovskite family have recently garnered interest for their correlated electron physics and strong sensitivity to external stimuli like strain, temperature, and even electric current. The bilayer ruthenate Ca₃Ru₂O₇ exhibits a structural distortion producing a polar metal and, under Ti substitution for Ru, a correlated antiferromagnetic insulator. Through low-temperature nano-infrared imaging, we reveal a spontaneous striped texture of coexisting insulating and metallic domains in single crystals across their insulator-metal phase transition at T=70-100K. Under in situ uniaxial strain, we image anisotropic nucleation and growth of these domains, rationalized through on-demand control of a spontaneous Jahn-Teller distortion. Through high resolution transmission electron microscopy, we also reveal the detailed interplay between this textured phase coexistence and the displacive orientations, volumetric structures, and domain boundaries among polar twin domains in these crystals. These novel imaging methods afford new insights into strain- and structure-mediated manipulation of the insulator-metal transition in 4d metal oxides and the ubiquity of phase coexistence even in pristine single crystals.