Electronic and optical properties of La-doped Sr${}_3$Ir${}_2$O${}_7$ epitaxial thin-films

Abstract

We have investigated structural, transport, and optical properties of tensile strained (Sr${}_{1-x}$La${}_x$)${}_3$Ir${}_2$O${}_7$ (x = 0, 0.025, 0.05) epitaxial thin-films. While High-T${}_c$ 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 Sr${}_3$Ir${}_2$O${}_7$ 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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