Structural Domain Imaging and Direct Determination of Crystallographic Orientation in Noncentrosymmetric Ca$_{3}$Ru$_{2}$O$_{7}$ Using Polarized Light Reflectance
1Key Laboratory of Artificial Structures and Quantum Control, and Shanghai Center for Complex Physics, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China 2Department of Physics and Engineering Physics, Tulane University, New Orleans 70118, USA 3Department of Physics, Pennsylvania State University, University Park, PA 16802, USA 4Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
Abstract：The noncentrosymmetricity of a prototypical correlated electron system Ca$_{3}$Ru$_{2}$O$_{7}$ renders extensive interest in the possible polar metallic state, along with multiple other closely competing interactions. However, the structural domain formation in this material often complicates the study of intrinsic material properties. It is crucial to fully characterize the structural domains for unrevealing underlying physics. Here, we report the domain imaging on Ca$_{3}$Ru$_{2}$O$_{7}$ crystal using the reflection of polarized light at normal incidence. The reflection anisotropy measurement utilizes the relative orientation between electric field component of the incident polarized light and the principal axis of the crystal, and gives rise to a peculiar contrast. The domain walls are found to be the interfaces between 90$^{\circ}$ rotated twin crystals by complementary magnetization measurements. A distinct contrast in reflectance is also found in the opposite cleavage surfaces, owing to the polar mode of the RuO$_{6}$ octahedra. More importantly, the analysis of the contrast between all inequivalent cleavage surfaces enables a direct determination of the crystallographic orientation of each domain. Such an approach provides an efficient yet feasible method for structural domain characterization, which can also find applications in noncentrosymmetric crystals in general.
2020, Vol. 37 
