Phase-Sensitive Observation of a Spin-Orbital Mott State in Sr
            <sub>2</sub>
            IrO
            <sub>4</sub>

Kim, Beomjoon; Ohsumi, H.; Komesu, Takashi; Sakai, Shiro; Morita, Toshiyuki; Takagi, H.; Arima, T.

doi:10.1126/science.1167106

Cited by 1,151 publications

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“…The conduction band mainly consists of the j eff = 1 2 character, and the energy gap is created by the AFM order, consistent with the previous studies. 13,14,22 Now we consider the particle-hole Green's function defined by…”

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confidence: 99%

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

Igarashi

Nagao

2014

J. Phys. Soc. Jpn.

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We study the elementary excitations in 5d transition metal oxide Sr2IrO4 by calculating the particle-hole Green's function within the random phase approximation on an antiferromagnetic ground state in the two-dimensional multi-orbital Hubbard model. The obtained magnetic excitations of bound states show a characteristic dispersion in consistent with the experiments. In addition, two new types of excitations are found due to the interplay between spin-orbit interaction and Hund's coupling: a magnetic excitation as a bound state, which has energy gap at the Γ point, and an exciton as a resonant mode in the continuum of electron-hole pair creation.Electron correlation effects on transition metals and their compounds have attracted much interest since the discovery of high-T C cuprate superconductors. In the 3d transition metal ions, the spin orbit interaction (SOI) plays a minor role on the electronic structures, since it is usually much smaller than the on-site Coulomb interaction and the crystal field splitting. In the 5d transition metal ions, however, the SOI is one order of magnitude larger than that of the 3d systems while the Coulomb interaction becomes weaker due to the extended nature of the 5d electrons. Accordingly, the interplay between the electron correlation and the SOI is expected to bring about new intriguing phenomena. For this reason, much attention has recently been paid to Ir oxides such as Sr 2 IrO 4 1-8 and Na 2 IrO 3 . [9][10][11][12] In particular, we focus on Sr 2 IrO 4 , which consists of two-dimensional IrO 2 layers showing structural similarity to the parent compound of high-T C cuprate La 2 CuO 4 , and exhibits a canted antiferromagnetic (AFM) order below 230 K. 1-3 The energy of the e g orbitals is estimated about 2 eV higher than that of the t 2g orbitals due to the large crystal field. Five 5d electrons are occupied per Ir atom, and one hole is sitting in the t 2g orbitals. Since the hole states have an effective orbital angular momentum ℓ equal to −1, the lowest-energy states on the localized electron picture are doubly degenerate with the effective total angular momentum j eff = 1 2 under the SOI: 13,14 |φ ± = 1 √ 3 (|yz, ∓σ ± i|zx, ∓σ ± |xy, ±σ ), where yz, zx, and xy designate t 2g orbitals, and spin component σ =↑. By introducing the isospin operators acting on these states, the system is mapped onto the Heisenberg model, from which an insulating AFM phase is derived, consistent with the experiments. 1-3 Furthermore, it has been pointed out that the small anisotropic terms emerge in addition to the isotropic term, when Hund's coupling is taken into account in the second-order process in the strong coupling expansion. 15,16 Recently, resonant inelastic x-ray scattering (RIXS) experiment at the Ir L edge has detected the excitation spectra, 17 whose low energy part follows the dispersion relation similar to the spin wave in the Heisenberg model on a square lattice. A notable point is that the excitation energy at the M point is nearly half of that at the X point, in contrast to t...

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confidence: 99%

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

Igarashi

Nagao

2014

J. Phys. Soc. Jpn.

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“…A host of particularly interesting physical phenomena may occur at the crossroads of these two energy scales [1,2,3,4]. For the case of Ir 4+ ions, where relativistic effects are significant and for a low-spin d 5 configuration in the presence of an octahedral crystal field, a four-fold degenerate J ef f = 3/2 multiplet and a two-fold degenerate J ef f = 1/2 multiplet are created.…”

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“…Figure 4 shows calculations for the three IRs, In order to determine the orientation of magnetic moments for both domains, we measured the intensity of ( 1 2 , 1 2 ,23) and ( 1 2 , 1 2 ,24) magnetic reflections as a function of the analyser rotation, η, in a horizontal scattering geometry (with π polarised incident x-rays) at T=90 K at the Ir L 3 edge. Data were collected over a wide range of azimuthal angles, Ψ and fitted to equation (1), these are shown in panels (a) and (c) of Figure 5 for the L=23,24 reflections, respectively. FDMNES calculations based on the Γ 2 representation were performed in order to model this experimental data and these are shown in panels (b) and (d).…”

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On the magnetic structure of Sr₃Ir₂O₇: an x-ray resonant scattering study

Boseggia

Springell

Walker

et al. 2012

J. Phys.: Condens. Matter

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Abstract. This report presents azimuthal dependent and polarisation dependent xray resonant magnetic scattering at the Ir L 3 edge for the bilayered iridate compound, Sr 3 Ir 2 O 7 . Two magnetic wave vectors, k 1 =( 1 2 , 1 2 ,0) and k 2 =( 1 2 ,-1 2 ,0), result in domains of two symmetry-related G-type antiferromagnetic structures, noted A and B, respectively. These domains are approximately 0.02 mm 2 and are independent of the thermal history. An understanding of this key aspect of the magnetism is necessary for an overall picture of the magnetic behaviour in this compound. Azimuthal and polarisation dependence of magnetic reflections, relating to both magnetic wave vectors, show that the Ir magnetic moments in the bilayer compound are oriented along the c axis. This contrasts with single layer Sr 2 IrO 4 where the moments are confined to the ab plane.

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“…Thus, the observed magnetic insulator ground state should be associated with the J eff = 1/2 state driven by a strong SOC, and can be understood generally in terms of the bandwidth narrowing. As mentioned in the Introduction, the ground state of the Ruddlesden-Popper series Sr n+1 Ir n O 3n+1 (n = 1, 2, ) evolves from the magnetic insulators for Sr 2 [12]. However, further studies are required in order to understand whether the microscopic interactions responsible for the magnetic ordering are similar in the random diluted three-dimensional SrIrO 3 perovskite and the well-ordered quasi-two-dimensional iridates.…”

Section: -3 Jps Conf Proc 013014 (2014)mentioning

confidence: 99%

“…Recently, the perovskite iridates have attracted much attention due to the formation of a novel J eff = 1/2 state associated with a large spin-orbital coupling (SOC) [1,2]. In order to explain the insulating ground state of Sr 2 IrO 4 , Kim et al [1] proposed that the strong SOC splits the otherwise broad t 2g band of the octahedral-site, low-spin Ir 4+ (5d 5 ) array into a filled, low-energy J eff = 3/2 quartet band and a half-filled, high-energy J eff = 1/2 doublet band, which can open a Mott gap by a moderate on-site Hubbard U, leading to a novel SOC-driven Mott insulating state.…”

Section: Introductionmentioning

confidence: 99%

Weak Ferromagnetism in the Orthorhombic Perovskite SrIr_0.8Sn_0.2O₃

Cheng¹,

Zhou²,

Goodenough³

et al. 2014

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013)

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We present a comparative study on the structure, resistivity, and magnetic properties of a SrIrO 3 and a 20% Sn-doped SrIr 0.8 Sn 0.2 O 3 perovskite both stabilized under high-pressure and high-temperature conditions. We found that the substitution of isovalent, nonmagnetic Sn 4+ for Ir 4+ ions converts the ground state from a paramagnetic metal for SrIrO 3 to a weak ferromagnetic insulator with high transition temperature T c = 280 K for SrIr 0.8 Sn 0.2 O 3 . For the later compound, a temperature-driven conductor-to-insulator transition at T c clearly evidenced a band gap opening associated with the spin ordering.

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Phase-Sensitive Observation of a Spin-Orbital Mott State in Sr ₂ IrO ₄

Cited by 1,151 publications

References 7 publications

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

On the magnetic structure of Sr₃Ir₂O₇: an x-ray resonant scattering study

Weak Ferromagnetism in the Orthorhombic Perovskite SrIr_0.8Sn_0.2O₃

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Phase-Sensitive Observation of a Spin-Orbital Mott State in Sr 2 IrO 4

Cited by 1,151 publications

References 7 publications

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr2IrO4

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr2IrO4

On the magnetic structure of Sr3Ir2O7: an x-ray resonant scattering study

Weak Ferromagnetism in the Orthorhombic Perovskite SrIr0.8Sn0.2O3

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Phase-Sensitive Observation of a Spin-Orbital Mott State in Sr ₂ IrO ₄

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

Interplay between Hund’s Coupling and Spin–Orbit Interaction on Elementary Excitations in Sr₂IrO₄

On the magnetic structure of Sr₃Ir₂O₇: an x-ray resonant scattering study

Weak Ferromagnetism in the Orthorhombic Perovskite SrIr_0.8Sn_0.2O₃