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

TL;DR

This study examines the structural, optical, and transport properties of La-doped Sr$_3$Ir$_2$O$_7$ thin films, revealing persistent insulating behavior and structural defects that influence their electronic properties.

Contribution

It provides new insights into the effects of La doping and structural defects on the electronic properties of Sr$_3$Ir$_2$O$_7$ thin films, contrasting with bulk crystal behavior.

Findings

All samples remain insulating with finite optical gaps.

Structural defects like stacking faults are observed.

La doping does not induce metallicity as in bulk crystals.

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.