Optical Properties of Electrochemically Gated La_(1?x)Sr_xCoO_(3? ) as a Topotactic Phase-Change Material

摘要

Materials with tunable infrared refractive index changes have enabled activemetasurfaces for novel control of optical circuits, thermal radiation, and more.Ion-gel-gated epitaxial films of the perovskite cobaltite La_(1?x)Sr_xCoO_(3? )(LSCO) with 0.00 ≤ x ≤ 0.70 offer a new route to significant, voltage-tuned,nonvolatile refractive index modulation for infrared active metasurfaces,shown here through Kramers–Kronig-consistent dispersion models, structuraland electronic transport characterization, and electromagnetic simulationsbefore and after electrochemical reduction. As-grown perovskite films arehigh-index insulators for x 0.18, due to apercolation insulator-metal transition. Positive-voltage gating of LSCOtransistors with x > 0.18 reveals a metal-insulator transition from the metallicperovskite phase to a high-index (n > 2.5), low-loss insulating phase,accompanied by a perovskite to oxygen-vacancy-ordered brownmilleritetransformation at high x. At x 0.6. Insimulations of plasmonic metasurfaces, these metal-insulator andinsulator-insulator transitions support significant, varied mid-infraredreflectance modulation, thus framing electrochemically gated LSCO as adiverse library of room-temperature phase-change materials for applicationsincluding dynamic thermal imaging, camouflage, and optical memories.