Optical signatures of spin-orbit exciton in bandwidth-controlled 
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 epitaxial films via high-concentration Ca and Ba doping

Souri, Maryam; Kim, B. H.; Gruenewald, J. H.; Connell, John; Thompson, J.; Nichols, John; Terzic, Jasminka; Min, B. I.; Cao, Gang; Brill, J. W.; Seo, S. S. A.

doi:10.1103/physrevb.95.235125

Cited by 20 publications

(17 citation statements)

References 35 publications

(46 reference statements)

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“…The strain appears to modulate the electron-hole bandwidth, and a large increase in the size of the gap at Q = (0,0) is observed upon tensile strain. We note that the hardening of peak A resembles the evolution of the "α-peak" observed in optical spectroscopy that was associated with a reduction of the U/t ratio (26,61). In particular, Nichols et al (26) found the optical gap to increase (decrease) upon tensile (compressive) strain.…”

Section: Resultssupporting

confidence: 61%

Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄

Paris

Tseng

Pärschke

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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In the high spin–orbit-coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr2IrO4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling.

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Section: Resultssupporting

confidence: 61%

Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄

Paris

Tseng

Pärschke

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Microscopic model Hamiltonians are generally superior to DFT-like approaches in capturing the dominant physics and offer a transparent interpretation of the main interactions, but restrictions on the cluster size and the dependence on adjustable interacting parameters could limit the accuracy of the results. Within these limits, the obtained optical conductivity, only available for Sr 2 IrO 4 , are in good agreement with experiments [43,50,54]. DFT-based schemes can provide an atomistic interpretation by solving a simplified Schrödinger equation and the DFT+U variant (with suitable values of the on-site parameter U) reproduces relatively well the value of the gap and the two-peak structure in Sr 2 IrO 4 [21,30].…”

Section: Introductionsupporting

confidence: 78%

Relativistic GW +BSE study of the optical properties of Ruddlesden-Popper iridates

Liu

Kim

Chen

et al. 2018

Phys. Rev. Materials

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We study the optical properties of the Ruddlesden-Popper series of iridates Sr n+1 Ir n O 3n+1 (n=1, 2 and ∞) by solving the Bethe-Salpeter equation (BSE), where the quasiparticle (QP) energies and screened interactions W are obtained by the GW approximation including spin-orbit coupling. The computed optical conductivity spectra show strong excitonic effects and reproduce very well the experimentally observed double-peak structure, in particular for the spin-orbital Mott insulators Sr 2 IrO 4 and Sr 3 Ir 2 O 7 . However, GW does not account well for the correlated metallic state of SrIrO 3 owing to a much too small band renormalization, and this affects the overall quality of the optical conductivity. Our analysis describes well the progressive redshift of the main optical peaks as a function of dimensionality (n), which is correlated with the gradual decrease of the electronic correlation (quantified by the constrained random phase approximation) towards the metallic n = ∞ limit. We have also assessed the quality of a computationally cheaper BSE approach that is based on a model dielectric function and conducted on top of DFT+U one-electron energies. Unfortunately, this model BSE approach does not accurately reproduce the outcome of the full GW+BSE method and leads to larger deviations to the measured spectra.arXiv:1806.07280v2 [cond-mat.str-el] 1 Aug 2018

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“…Since the low-energy optical absorption is understood as an optical transition from the lower Hubbard band to the upper Hubbard band of the Jeff = 1/2 state, i.e. the Mott-Hubbard gap, its energy is proportional to U/t [14,30]. This observation has been debated because compressive strain is expected to decrease θ and t, as generally believed in the rigid octahedral picture of transition metal oxides.…”

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confidence: 99%

Compressive strain induced enhancement of exchange interaction and short-range magnetic order in Sr2IrO4 investigated by Raman spectroscopy

et al. 2019

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We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr2IrO4 under in-plane misfit strain. With in-plane biaxial compression, the energy of the two-magnon peak increases, and the peak remains observable over a wider temperature range above the Néel temperature, indicating strain-induced enhancement of the superexchange interactions between Jeff = 1/2 pseudospins. From density functional theory calculations, we have found an increase of the nearest-neighbor hopping parameter and exchange interaction with increasing biaxial compressive strain, in agreement with the experimental observations. Our experimental and theoretical results provide perspectives for systematic, theory-guided strain control of the primary exchange interactions in 5d transition metal oxides.

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Optical signatures of spin-orbit exciton in bandwidth-controlled Sr2IrO4 epitaxial films via high-concentration Ca and Ba doping

Cited by 20 publications

References 35 publications

Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄

Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄

Relativistic GW +BSE study of the optical properties of Ruddlesden-Popper iridates

Compressive strain induced enhancement of exchange interaction and short-range magnetic order in Sr2IrO4 investigated by Raman spectroscopy

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Optical signatures of spin-orbit exciton in bandwidth-controlled Sr2IrO4 epitaxial films via high-concentration Ca and Ba doping

Cited by 20 publications

References 35 publications

Strain engineering of the charge and spin-orbital interactions in Sr 2 IrO 4

Strain engineering of the charge and spin-orbital interactions in Sr 2 IrO 4

Relativistic GW +BSE study of the optical properties of Ruddlesden-Popper iridates

Compressive strain induced enhancement of exchange interaction and short-range magnetic order in Sr2IrO4 investigated by Raman spectroscopy

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Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄

Strain engineering of the charge and spin-orbital interactions in Sr ₂ IrO ₄