Direct Imaging of Submicron Scale Defect-induced Birefringence in SrTiO$_{3}$ Bicrystals

Using a near-field scanning optical microscope capable of quantitative polarimetry, we map the anisotropic strain fields associated with individual submicron defects near the fusion boundaries of SrTiO$_{3}$ bicrystals. Many defects exhibit unexpected spiral-shape strain patterns, whose handedness is believed to be linked to the bicrystal synthesis process. Direct observation of these defect-induced strain fields helps explain previously observed non-uniformity in the characteristics of high temperature superconductor grain boundary junctions fabricated on SrTiO$_{3}$ bicrystals.