Electronic and optical properties of La-doped Sr3Ir2O7 epitaxial thin films

Abstract

We have investigated structural, transport, and optical properties of tensile strained (Sr1-xLax)3Ir2O7 (x = 0, 0.025, 0.05) epitaxial thin-films. While High-Tc superconductivity is predicted theoretically in the system, we have observed that all of the samples remain insulating with finite optical gap energies and Mott variable-range hopping characteristics in transport. Cross-sectional scanning transmission electron microscopy indicates that structural defects such as stacking faults appear in this system. The insulating behavior of the La-doped Sr3Ir2O7 thin-films is presumably due to disorder-induced localization and ineffective electron-doping of La, which brings to light the intriguing difference between epitaxial thin films and bulk single crystals of the iridates.

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“…36–38 However, no metallic state is observed in the doped iridate thin films with a chemical dopant. 39–41 The difference is presumably due to the ineffective doping effect of the doped iridate films because the chemical and structural disorder by element substitutions become larger under epitaxial strain. As known, IL gating is considered a promising approach to realize effective electrostatic doping with minimized chemical and structural variations.…”