Abstract
The 4d transition metal perovskites Can+1RunO3n+1 have attracted interest for their strongly interacting electronic phases showing pronounced sensitivity to controllable stimuli like strain, temperature, and even electrical current. Through multi-messenger low-temperature nano-imaging, we reveal a spontaneous striped texture of coexisting insulating and metallic domains in single crystals of the bilayer ruthenate Ca3(TixRu1-x)2O7 across its first-order Mott transition at T approx 95K. We image on-demand anisotropic nucleation and growth of these domains under in situ applied uniaxial strain rationalized through control of a spontaneous Jahn-Teller distortion. Our scanning nano-susceptibility imaging resolves the detailed susceptibility of coexisting phases to strain and temperature at the transition threshold. Comparing these nano-imaging results to bulk-sensitive elastoresistance measurements, we uncover an emergent “domain susceptibility” sensitive to both the volumetric phase fractions and elasticity of the self-organized domain lattice. Our combined susceptibility probes afford nano-scale insights into strain-mediated control over the insulator-metal transition in 4d transition metal oxides.
Highlights
Many of the most exotic physical phenomena manifesting in the solid state are expressed in transition metal oxides, where the interaction of electronic, spin, and lattice degrees of freedom produce “soft” electronic states modified by external perturbations[1,2]
To enable studying the response of the phase transition to in situ applied strain, individual floating-zone-grown CTRO single crystals of characteristic dimension 100 × 100 × 10 microns[3] were glued with their long dimension across the 50-micron gap between the two shear piezoelectric stacks of a home-built uniaxial strain stage (Fig. 1a). With this “strain stage”, relative displacements of ~±1 micron can be achieved between the two shear stacks at their top surface with a differential bias of ±500 V at a temperature of T ~ 100 K, enabling application of quasi-uniform uniaxial strains exceeding ±2% to samples of similar to the change in work function through the insulator-metal transition of an analogous correlated oxide, VO249, affirming our assignment of insulator and metal domains based on infrared contrast
Work function variations show no noticeable association with the local surface topography (Fig. 1f, right), which is atomically smooth to the precision of our atomic force microscope (AFM), with exception of notable buckling in the crystal surface on the scale of several nanometers associated directly with the suitable dimension
Summary
Many of the most exotic physical phenomena manifesting in the solid state are expressed in transition metal oxides, where the interaction of electronic, spin, and lattice degrees of freedom produce “soft” electronic states modified by external perturbations[1,2] Celebrated hosts for these highly tunable phenomena include copper oxide high-Tc superconductors, colossal magnetoresistive manganites[3], polar materials like ferroelectrics and ferromagnets[4], and Mott insulators poised near an insulator-metal transition (IMT). “Active” strain control through direct mechanical actuation of phase transitions in single crystals[18,19,20,21] including the insulator-metal transition of 3d metal oxides[9,22] can provide a wealth of insights into the elastic susceptibility of functional electronic phases This approach has recently been leveraged to explore lattice coupling of competing phases in the 4d ruthenates[23,24]. We demonstrate the emergence of an elastic susceptibility associated directly with domain configurations of phases coexisting in a spontaneous nano-texture across the IMT of a prototypic Mott crystal—Tisubstituted Ca3(TixRu1-x)2O7 (hereafter denoted CTRO)
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