Quasi-periodic metal-insulator phase separation in strain engineered La_0.66Sr_0.33MnO₃ thin films

We report the electronic phase separation in the prototypical double exchange ferromagnet La_0.66Sr_0.33MnO₃ (LSMO) thin films grown on LaAlO₃ (LAO) substrate. We discovered a peculiar mesoscale stripe pattern that only occurs at specific film thickness, using the scattering-type scanning near-field optical microscope (s-SNOM) at the mid-infrared (mid-IR) frequencies. These novel quasi-periodic mesoscale metal-insulator-metal stripes are contributed to a subtle and delicate balance between the epitaxial strain and surface twin structure of the LAO substrate. Our work strongly suggests the possibility to control the metallicity via interface and strain engineering in strontium doped manganites.