Optical Signatures of Spin-Orbit Exciton in Bandwidth Controlled Sr${}_2$IrO${}_4$ Epitaxial Films via High-Concentration Ca and Ba Doping

Abstract

We have investigated the electronic and optical properties of (Sr${}_{1-x}$Ca${}_x$)${}_2$IrO${}_4$ (x= 0 - 0.375) and (Sr${}_{1-y}$Ba${}_y$)${}_2$IrO${}_4$ (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 Sr${}_2$IrO${}_4$. As the average A-site ionic radius increases from (Sr${}_{1-x}$Ca${}_x$)${}_2$IrO${}_4$ to (Sr${}_{1-y}$Ba${}_y$)${}_2$IrO${}_4$, 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 inter-site optical transitions within the J${}_{eff}$= 1/2 band. Our experimental results are consistent with this interpretation as implemented by a multi-orbital Hubbard model calculation: namely, incorporating a strong Fano-like coupling between the spin-orbit exciton and inter-site d-d transitions within the J${}_{eff}$= 1/2 band.

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Cited by in corpus (13)

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• Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4
• The Jeff=1/2 antiferromagnet Sr2IrO4: A golden avenue toward new physics and functions
• Compressive-strain induced enhancement of exchange interactions and short-range magnetic order in Sr${}_2$IrO${}_4$ investigated by Raman spectroscopy
• Nanoscale Sr${}_2$IrO${}_4$ Freestanding Thin-Films for Flexible Electronics
• BCS-BEC crossover in a $(t_{2g}{)}^4$ Excitonic Magnet
• Optical Signature of a Crossover from Mott- to Slater-type Gap in Sr${}_2$Ir${}_{1-x}$Rh${}_x$O${}_4$
• Magnetism and electrical transport in Y-doped layered iridate Sr${}_2$IrO${}_4$
• Decoupling of magnetism and electric transport in single-crystal (Sr1-xAx)2IrO4 (A = Ca or Ba)
• Novel Block Excitonic Condensate at $n=3.5$ in a Spin-Orbit Coupled $t_{2g}$ Multiorbital Hubbard Model
• Electronic and optical properties of La-doped Sr${}_3$Ir${}_2$O${}_7$ epitaxial thin-films
• Possible superconductivity induced by a large spin-orbit coupling in carrier doped iridium oxide insulators: A weak coupling approach
• Coupled spin-orbital fluctuations in a three orbital model for $4d$ and $5d$ oxides with electron fillings $n=3,4,5$ -- Application to $\mathrm{NaOs}{\mathrm{O}}_3$, $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$, and $\mathrm{S}{\mathrm{r}}_2\mathrm{Ir}{\mathrm{O}}_4$