We have investigated the electronic and optical properties of (Sr1-xCax)2IrO4 (x=0-0.375) and (Sr1-yBay)2IrO4 (y=0-0.375) epitaxial thin films, in which the bandwidth is systematically tuned via chemical substitutions of Sr ions by Ca and Ba. Transport measurements indicate that the thin-film series exhibits insulating behavior, similar to the Jeff=1/2 spin-orbit Mott insulator Sr2IrO4. As the average A-site ionic radius increases from (Sr1-xCax)2IrO4 to (Sr1-yBay)2IrO4, optical conductivity spectra in the near-infrared region shift to lower energies, which cannot be explained by the simple picture of well-separated Jeff=1/2 and Jeff=3/2 bands. We suggest that the two-peak-like optical conductivity spectra of the layered iridates originates from the overlap between the optically forbidden spin-orbit exciton and the intersite optical transitions within the Jeff=1/2 band. Our experimental results are consistent with this interpretation as implemented by a multiorbital Hubbard model calculation: namely, incorporating a strong Fano-like coupling between the spin-orbit exciton and intersite d-d transitions within the Jeff=1/2 band.
|Journal||Physical Review B|
|State||Published - Jun 14 2017|
Bibliographical noteFunding Information:
We thank C. H. Sohn for useful discussions and valuable comments. We acknowledge the support of National Science Foundation 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. B.H.K. acknowledges support from the RIKEN iTHES Project for the numerical calculations.
© 2017 American Physical Society.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics