Optical Signatures of Spin-Orbit Exciton in Bandwidth-Controlled Sr₂IrO₄ Epitaxial Films via High-Concentration Ca and Ba Doping

Authors

Maryam Souri, University of KentuckyFollow
B. H. Kim, Pohang University of Science and Technology, South Korea
John H. Gruenewald, University of KentuckyFollow
John G. Connell, University of KentuckyFollow
J. Thompson, University of Kentucky
J. Nichols, University of Kentucky
Jsaminka Terzic, University of KentuckyFollow
B. I. Min, Pohang University of Science and Technology, South Korea
Gang Cao, University of KentuckyFollow
Joseph W. Brill, University of KentuckyFollow
Sung S. Ambrose Seo, University of KentuckyFollow

Abstract

We have investigated the electronic and optical properties of (Sr_1−xCa_x)₂IrO₄ (x = 0–0.375) and (Sr_1−yBa_y)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 J_eff = 1/2 spin-orbit Mott insulator Sr₂IrO₄. As the average A-site ionic radius increases from (Sr_1−xCa_x)₂IrO₄ to (Sr_1−yBa_y)₂IrO₄, optical conductivity spectra in the near-infrared region shift to lower energies, which cannot be explained by the simple picture of well-separated J_eff = 1/2 and J_eff = 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 J_eff = 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 J_eff = 1/2 band.

Document Type

Article

Publication Date

6-14-2017

Notes/Citation Information

Published in Physical Review B, v. 95, issue 23, 235125, p. 1-7.

©2017 American Physical Society

The copyright holder has granted permission for posting the article here.

Digital Object Identifier (DOI)

https://doi.org/10.1103/PhysRevB.95.235125

Funding Information

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.

Repository Citation

Souri, Maryam; Kim, B. H.; Gruenewald, John H.; Connell, John G.; Thompson, J.; Nichols, J.; Terzic, Jsaminka; Min, B. I.; Cao, Gang; Brill, Joseph W.; and Seo, Sung S. Ambrose, "Optical Signatures of Spin-Orbit Exciton in Bandwidth-Controlled Sr₂IrO₄ Epitaxial Films via High-Concentration Ca and Ba Doping" (2017). Physics and Astronomy Faculty Publications. 525.
https://uknowledge.uky.edu/physastron_facpub/525