Phonon-assisted optical excitation in the narrow bandgap Mott insulator Sr3Ir2O7

Abstract

We examined the temperature (T) evolution of the optical conductivity spectra of Sr${}_3$Ir${}_2$O${}_7$ over a wide range of 10-400 K. The system was barely insulating, exhibiting a small indirect bandgap of $\sim$0.1 eV. The low-energy features of the optical d-d excitation ($\hslash \omega$ $<$ 0.3 eV) evolved drastically, whereas such evolution was not observed for the O K-edge X-ray absorption spectra. This suggests that the T evolution in optical spectra is not caused by a change in the bare (undressed) electronic structure, but instead, presumably originates from an abundance of phonon-assisted indirect excitations. Our results showed that the low-energy excitations were dominated by phonon-absorption processes which involve, in particular, the optical phonons. This implies that phonon-assisted processes significantly facilitate the charge dynamics in barely insulating Sr${}_3$Ir${}_2$O${}_7$.

submitted to Phys. Rev. B

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• Relativistic $GW$+BSE study of the optical properties of Ruddlesden-Popper iridates
• A weakly correlated Fermi liquid state with a small Fermi surface in lightly doped Sr${}_3$Ir${}_2$O${}_7$
• Strong Pseudospin-Lattice Coupling in Sr3Ir2O7: Coherent Phonon Anomaly and Negative Thermal Expansion
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• Magnetic properties of bilayer Sr${}_3$Ir${}_2$O${}_7$: role of epitaxial strain and oxygen vacancies
• High-pressure insulator-to-metal transition in Sr${}_3$Ir${}_2$O${}_7$ studied by x-ray absorption spectroscopy
• Symmetry-resolved two-magnon excitations in a strong spin-orbit-coupled bilayer antiferromagnet
• Non-thermal breaking of magnetic order via photo-generated spin defects
• Metal-Insulator Transitions and non-Fermi Liquid Behaviors in 5d Perovskite Iridates
• Spin-lattice and electron-phonon coupling in 3$d$/5$d$ hybrid Sr${}_3$NiIrO${}_6$
• Electronic and optical properties of La-doped Sr${}_3$Ir${}_2$O${}_7$ epitaxial thin-films
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