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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Published in Physical Review Materials, v. 2, issue 2, 024803, p. 1-6.

©2018 American Physical Society

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We acknowledge the support of NSF Grants No. DMR-1454200 (for thin-film synthesis and characterizations), No. DMR-1265162 and No. DMR-1712101 (for target synthesis), and No. DMR-1262261 (for infrared spectroscopy).