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Kim H, Kim JK, Kwon J, Kim J, Kim HWJ, Ha S, Kim K, Lee W, Kim J, Cho GY, Heo H, Jang J, Sahle CJ, Longo A, Strempfer J, Fabbris G, Choi Y, Haskel D, Kim J, Kim JW, Kim BJ. Quantum spin nematic phase in a square-lattice iridate. Nature 2024; 625:264-269. [PMID: 38093009 DOI: 10.1038/s41586-023-06829-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Accepted: 11/03/2023] [Indexed: 01/12/2024]
Abstract
Spin nematic is a magnetic analogue of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid1,2. Particularly intriguing is a valence-bond spin nematic3-5, in which spins are quantum entangled to form a multipolar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. Here we establish a spin nematic phase in the square-lattice iridate Sr2IrO4, which approximately realizes a pseudospin one-half Heisenberg antiferromagnet in the strong spin-orbit coupling limit6-9. Upon cooling, the transition into the spin nematic phase at TC ≈ 263 K is marked by a divergence in the static spin quadrupole susceptibility extracted from our Raman spectra and concomitant emergence of a collective mode associated with the spontaneous breaking of rotational symmetries. The quadrupolar order persists in the antiferromagnetic phase below TN ≈ 230 K and becomes directly observable through its interference with the antiferromagnetic order in resonant X-ray diffraction, which allows us to uniquely determine its spatial structure. Further, we find using resonant inelastic X-ray scattering a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a many-body quantum entanglement in the antiferromagnetic state10,11. Taken together, our results reveal a quantum order underlying the Néel antiferromagnet that is widely believed to be intimately connected to the mechanism of high-temperature superconductivity12,13.
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Affiliation(s)
- Hoon Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Jin-Kwang Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Junyoung Kwon
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Jimin Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Hyun-Woo J Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Seunghyeok Ha
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Kwangrae Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Wonjun Lee
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Jonghwan Kim
- Center for Van der Waals Quantum Solids, Institute for Basic Science, Pohang, Korea
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Korea
| | - Gil Young Cho
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea
| | - Hyeokjun Heo
- Department of Physics and Astronomy, Seoul National University, Seoul, South Korea
| | - Joonho Jang
- Department of Physics and Astronomy, Seoul National University, Seoul, South Korea
| | - C J Sahle
- ESRF, The European Synchrotron, Grenoble, France
| | - A Longo
- ESRF, The European Synchrotron, Grenoble, France
- Istituto per lo Studio dei Materiali Nanostrutturati (ISMN)-CNR, UOS Palermo, Palermo, Italy
| | - J Strempfer
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - G Fabbris
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - Y Choi
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - D Haskel
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - Jungho Kim
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - J -W Kim
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA
| | - B J Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, South Korea.
- Department of Physics, Pohang University of Science and Technology, Pohang, South Korea.
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Giant stress response of terahertz magnons in a spin-orbit Mott insulator. Nat Commun 2022; 13:6674. [DOI: 10.1038/s41467-022-34375-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 10/21/2022] [Indexed: 11/06/2022] Open
Abstract
AbstractMagnonic devices operating at terahertz frequencies offer intriguing prospects for high-speed electronics with minimal energy dissipation However, guiding and manipulating terahertz magnons via external parameters present formidable challenges. Here we report the results of magnetic Raman scattering experiments on the antiferromagnetic spin-orbit Mott insulator Sr2IrO4 under uniaxial stress. We find that the energies of zone-center magnons are extremely stress sensitive: lattice strain of 0.1% increases the magnon energy by 40%. The magnon response is symmetric with respect to the sign of the applied stress (tensile or compressive), but depends strongly on its direction in the IrO2 planes. A theory based on coupling of the spin-orbit-entangled iridium magnetic moments to lattice distortions provides a quantitative explanation of the Raman data and a comprehensive framework for the description of magnon-lattice interactions in magnets with strong spin-orbit coupling. The possibility to efficiently manipulate the propagation of terahertz magnons via external stress opens up multifold design options for reconfigurable magnonic devices.
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Abstract
Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr3Ir2O7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase. Antiferromagnetic excitonic insulators are a distinct form of excitonic insulator, in which electrons and holes are bound by magnetic exchange rather than Coulomb attraction. Here, Mazzone et al. show, using X-ray scattering, that Sr3Ir2O7 realizes this particular state.
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Ahn G, Schmehr JL, Porter Z, Wilson SD, Moon SJ. Doping and temperature evolutions of optical response of Sr 3(Ir 1-xRu x) 2O 7. Sci Rep 2020; 10:22340. [PMID: 33339856 PMCID: PMC7749133 DOI: 10.1038/s41598-020-79263-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 12/01/2020] [Indexed: 11/09/2022] Open
Abstract
We report on optical spectroscopic study of the Sr3(Ir1-xRux)2O7 system over a wide doping regime. We find that the changes in the electronic structure occur in the limited range of the concentration of Ru ions where the insulator-metal transition occurs. In the insulating regime, the electronic structure associated with the effective total angular momentum Jeff = 1/2 Mott state remains robust against Ru doping, indicating the localization of the doped holes. Upon entering the metallic regime, the Mott gap collapses and the Drude-like peak with strange metallic character appears. The evolution of the electronic structure registered in the optical data can be explained in terms of a percolative insulator-metal transition. The phonon spectra display anomalous doping evolution of the lineshapes. While the phonon modes of the compounds deep in the insulating and metallic regimes are almost symmetric, those of the semiconducting compound with x = 0.34 in close proximity to the doping-driven insulator-metal transition show a pronounced asymmetry. The temperature evolution of the phonon modes of the x = 0.34 compound reveals the asymmetry is enhanced in the antiferromagnetic state. We discuss roles of the S = 1 spins of the Ru ions and charge excitations for the conspicuous lineshape asymmetry of the x = 0.34 compound.
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Affiliation(s)
- Gihyeon Ahn
- Department of Physics, Hanyang University, Seoul, 04763, Republic of Korea
| | - J L Schmehr
- Materials Department, University of California, Santa Barbara, CA, 93106, USA
| | - Z Porter
- Materials Department, University of California, Santa Barbara, CA, 93106, USA
| | - S D Wilson
- Materials Department, University of California, Santa Barbara, CA, 93106, USA
| | - S J Moon
- Department of Physics, Hanyang University, Seoul, 04763, Republic of Korea. .,Research Institute of Natural Science, Hanyang University, Seoul, 04763, Republic of Korea.
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5
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Abstract
Understanding the relationship between entangled degrees of freedom (DOF) is a central problem in correlated materials and the possibility to influence their balance is promising toward realizing novel functionalities. In Sr2IrO4, the interaction between spin–orbit coupling and electron correlations induces an exotic ground state with magnetotransport properties promising for antiferromagnetic spintronics applications. Moreover, the coupling between orbital and spin DOF renders the magnetic structure sensitive to the Ir–O bond environment. To date, a detailed understanding of the microscopic spin-lattice and electron–phonon interactions is still lacking. Here, we use strain engineering to perturb the local lattice environment and, by tracking the response of the low-energy elementary excitations, we unveil the response of the microscopic spin and charge interactions. 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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Li S, Drueke E, Porter Z, Jin W, Lu Z, Smirnov D, Merlin R, Wilson SD, Sun K, Zhao L. Symmetry-Resolved Two-Magnon Excitations in a Strong Spin-Orbit-Coupled Bilayer Antiferromagnet. PHYSICAL REVIEW LETTERS 2020; 125:087202. [PMID: 32909791 DOI: 10.1103/physrevlett.125.087202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 07/29/2020] [Indexed: 06/11/2023]
Abstract
We used a combination of polarized Raman spectroscopy and spin wave calculations to study magnetic excitations in the strong spin-orbit-coupled bilayer perovskite antiferromagnet Sr_{3}Ir_{2}O_{7}. We observed two broad Raman features at ∼800 and ∼1400 cm^{-1} arising from magnetic excitations. Unconventionally, the ∼800 cm^{-1} feature is fully symmetric (A_{1g}) with respect to the underlying tetragonal (D_{4h}) crystal lattice which, together with its broad line shape, definitively rules out the possibility of a single magnon excitation as its origin. In contrast, the ∼1400 cm^{-1} feature shows up in both the A_{1g} and B_{2g} channels. From spin wave and two-magnon scattering cross-section calculations of a tetragonal bilayer antiferromagnet, we identified the ∼800 cm^{-1} (1400 cm^{-1}) feature as two-magnon excitations with pairs of magnons from the zone-center Γ point (zone-boundary van Hove singularity X point). We further found that this zone-center two-magnon scattering is unique to bilayer perovskite magnets which host an optical branch in addition to the acoustic branch, as compared to their single layer counterparts. This zone-center two-magnon mode is distinct in symmetry from the time-reversal symmetry broken "spin wave gap" and "phase mode" proposed to explain the ∼92 meV (742 cm^{-1}) gap in resonant inelastic x-ray spectroscopy magnetic excitation spectra of Sr_{3}Ir_{2}O_{7}.
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Affiliation(s)
- Siwen Li
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Elizabeth Drueke
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Zach Porter
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Wencan Jin
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Zhengguang Lu
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
- Department of Physics, Florida State University, Tallahassee, Florida 32310, USA
| | - Dmitry Smirnov
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
| | - Roberto Merlin
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Stephen D Wilson
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Kai Sun
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Liuyan Zhao
- Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
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Singh B, Kumar D, Manna K, Bera AK, Cansever GA, Maljuk A, Wurmehl S, Büchner B, Kumar P. Correlated paramagnetism and interplay of magnetic and phononic degrees of freedom in 3d-5d coupled La 2CuIrO 6. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:485803. [PMID: 31422956 DOI: 10.1088/1361-648x/ab3c14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Conventional paramagnetism-a state with finite magnetic moment per ion sans long range magnetic ordering, but with lowering temperature the moment each ion picks up a particular direction, breaking spin rotational symmetry, and results into long-range magnetic ordering. However, in systems with competing multiple degrees of freedom this conventional notion may easily break and results into short range correlation much above the global magnetic transition temperature. La2CuIrO6 with complex interplay of spins (s = 1/2) on Cu site and pseudo-spin (j = 1/2) on Ir site owing to strong spin-orbit coupling provides fertile ground to observe such correlated phenomena. By a comprehensive temperature dependent Raman study, we have shown the presence of such a correlated paramagnetic state in La2CuIrO6 much above the long-range magnetic ordering temperature (T N ). Our observation of strong interactions of phonons, associated with Cu/Ir octahedra, with underlying magnetic degrees of freedom mirrored in the observed Fano asymmetry, which remarkably persists as high as ~3.5T N clearly signals the existence of correlated paramagnetism hence broken spin rotational symmetry. Our detailed analysis also reveals anomalous changes in the self-energy parameters of the phonon modes, i.e. mode frequencies and linewidth, below T N , providing a useful gauge for monitoring the strong coupling between phonons and magnetic degrees of freedom.
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Affiliation(s)
- Birender Singh
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi 175005, India
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Abstract
Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various types of magnetic materials observed thus far by inelastic light scattering experiments. The anomalously large asymmetry of anti-Stokes to Stokes intensity ratio, broad linewidth, strong resonance effect, unique polarization selection, and abnormal impurity dependence of spin waves are discussed. In addition, the mechanisms of these anomalous behaviors of spin waves are proposed.
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9
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Liu XC, Li WQ, Wang YR, Zhou GN, Wang YX, He CS, Wang GM, Mu Y. Cathode-Introduced Atomic H* for Fe(II)-Complex Regeneration to Effective Electro-Fenton Process at a Natural pH. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:6927-6936. [PMID: 31117534 DOI: 10.1021/acs.est.9b00345] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Promotion of iron solubility using ligands is the preliminary step in the homogeneous electro-Fenton (EF) process at a mild pH, but the chelate efficiencies of most organic ligands are unsatisfactory, resulting in insufficient Fe(II) availability. In this study, atomic H* was, for the first time, introduced to the EF process to accelerate the regeneration of the Fe(II)-complex at a mild pH using a Ni-deposited carbon felt (Ni-CF) cathode. The introduction of atomic H* significantly elevated total organic carbon (TOC) abatement of ciprofloxacin (CIP) from 42% (CF) to 81% (Ni-CF) at a natural pH. In the presence of humic acids (HAs), atomic H* introduced via Ni-CF enhanced the CIP degradation rate to 10 times that of the CF at a mild pH. The electron spin resonance (ESR), density functional theory (DFT) calculations, electrochemical characterization, and in situ electrochemical Raman study clearly demonstrated that the atomic H* generated from the Ni-CF cathode was highly efficient at reducing Fe(III)-complexes at a natural pH. Additionally, the Ni-CF could generate atomic H* without significant nickel leaching. Thus, the atomic H* could continuously facilitate iron cycling and, consequently, enhance pollutant mineralization via the homogeneous EF process at a mild pH in an environmentally friendly manner.
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Affiliation(s)
- Xiao-Cheng Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Wen-Qiang Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Yi-Ran Wang
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Guan-Nan Zhou
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Yi-Xuan Wang
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Chuan-Shu He
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Gong-Ming Wang
- Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
| | - Yang Mu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry , University of Science & Technology of China , Hefei 230026 , China
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Vale JG, Boseggia S, Walker HC, Springell RS, Hunter EC, Perry RS, Collins SP, McMorrow DF. Critical fluctuations in the spin-orbit Mott insulator Sr 3Ir 2O 7. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:185803. [PMID: 30721882 DOI: 10.1088/1361-648x/ab0471] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
X-ray magnetic critical scattering measurements and specific heat measurements were performed on the perovskite iridate [Formula: see text]. We find that the magnetic interactions close to the Néel temperature [Formula: see text] are three-dimensional. This contrasts with previous studies which suggest two-dimensional behaviour like Sr2IrO4. Violation of the Harris criterion ([Formula: see text]) means that weak disorder becomes relevant. This leads a rounding of the antiferromagnetic phase transition at [Formula: see text], and modifies the critical exponents relative to the clean system. Specifically, we determine that the critical behaviour of [Formula: see text] is representative of the diluted 3D Ising universality class.
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Affiliation(s)
- J G Vale
- London Centre for Nanotechnology and Department of Physics and Astronomy, University College London (UCL), Gower Street, London, WC1E 6BT, United Kingdom. Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, CH-1015, Switzerland
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11
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Singh B, Cansever GA, Dey T, Maljuk A, Wurmehl S, Büchner B, Kumar P. Orbiton-phonon coupling in Ir 5+(5d 4) double perovskite Ba 2YIrO 6. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:065603. [PMID: 30523849 DOI: 10.1088/1361-648x/aaf40a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Ba2YIrO6, a Mott insulator, with four valence electrons in Ir5+ d-shell (5d 4) is supposed to be non-magnetic, with J eff = 0, within the atomic physics picture. However, recent suggestions of non-zero magnetism have raised some fundamental questions about its origin. We focus on the phonon dynamics, probed via Raman scattering, as a function of temperature and different incident photon energies, as an external perturbation. Our studies reveal strong renormalization of the phonon self-energy parameters and integrated intensity for first-order modes, especially redshift of the few first-order modes with decreasing temperature and anomalous softening of modes associated with IrO6 octahedra, as well as high energy Raman bands attributed to the strong anharmonic phonons and coupling with orbital excitations. The distinct renormalization of second-order Raman bands with respect to their first-order counterpart suggest that higher energy Raman bands have significant contribution from orbital excitations. Our observation indicates that strong anharmonic phonons coupled with electronic/orbital degrees of freedom provides a knob for tuning the conventional electronic levels for 5d-orbitals, and this may give rise to non-zero magnetism as postulated in recent theoretical calculations with rich magnetic phases.
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Affiliation(s)
- Birender Singh
- School of Basic Sciences, Indian Institute of Technology Mandi, Mandi 175005, India
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12
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Liu H, Khaliullin G. Pseudo-Jahn-Teller Effect and Magnetoelastic Coupling in Spin-Orbit Mott Insulators. PHYSICAL REVIEW LETTERS 2019; 122:057203. [PMID: 30822030 DOI: 10.1103/physrevlett.122.057203] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 11/22/2018] [Indexed: 06/09/2023]
Abstract
The consequences of the Jahn-Teller (JT) orbital-lattice coupling for magnetism of pseudospin J_{eff}=1/2 and J_{eff}=0 compounds are addressed. In the former case, represented by Sr_{2}IrO_{4}, this coupling generates, through the so-called pseudo-JT effect, orthorhombic deformations of a crystal concomitant with magnetic ordering. The orthorhombicity axis is tied to the magnetization and rotates with it under magnetic field. The theory resolves a number of puzzles in Sr_{2}IrO_{4} such as the origin of in-plane magnetic anisotropy and magnon gaps, metamagnetic transition, etc. In J_{eff}=0 systems, the pseudo-JT effect leads to spin-nematic transition well above magnetic ordering, which may explain the origin of "orbital order" in Ca_{2}RuO_{4}.
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Affiliation(s)
- Huimei Liu
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Giniyat Khaliullin
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
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13
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Cao G, Schlottmann P. The challenge of spin-orbit-tuned ground states in iridates: a key issues review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:042502. [PMID: 29353815 DOI: 10.1088/1361-6633/aaa979] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb and crystalline electric field interactions in iridates drives exotic quantum states that are unique to this group of materials. In particular, the 'J eff = ½' Mott state served as an early signal that the combined effect of strong spin-orbit and Coulomb interactions in iridates has unique, intriguing consequences. In this Key Issues Review, we survey some current experimental studies of iridates. In essence, these materials tend to defy conventional wisdom: absence of conventional correlations between magnetic and insulating states, avoidance of metallization at high pressures, 'S-shaped' I-V characteristic, emergence of an odd-parity hidden order, etc. It is particularly intriguing that there exist conspicuous discrepancies between current experimental results and theoretical proposals that address superconducting, topological and quantum spin liquid phases. This class of materials, in which the lattice degrees of freedom play a critical role seldom seen in other materials, evidently presents some profound intellectual challenges that call for more investigations both experimentally and theoretically. Physical properties unique to these materials may help unlock a world of possibilities for functional materials and devices. We emphasize that, given the rapidly developing nature of this field, this Key Issues Review is by no means an exhaustive report of the current state of experimental studies of iridates.
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Affiliation(s)
- Gang Cao
- Department of Physics, University of Colorado at Boulder, Boulder, CO 80309, United States of America
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14
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Kung HH, Maiti S, Wang X, Cheong SW, Maslov DL, Blumberg G. Chiral Spin Mode on the Surface of a Topological Insulator. PHYSICAL REVIEW LETTERS 2017; 119:136802. [PMID: 29341673 DOI: 10.1103/physrevlett.119.136802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2017] [Indexed: 05/05/2023]
Abstract
Using polarization-resolved resonant Raman spectroscopy, we explore collective spin excitations of the chiral surface states in a three dimensional topological insulator, Bi_{2}Se_{3}. We observe a sharp peak at 150 meV in the pseudovector A_{2} symmetry channel of the Raman spectra. By comparing the data with calculations, we identify this peak as the transverse collective spin mode of surface Dirac fermions. This mode, unlike a Dirac plasmon or a surface plasmon in the charge sector of excitations, is analogous to a spin wave in a partially polarized Fermi liquid, with spin-orbit coupling playing the role of an effective magnetic field.
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Affiliation(s)
- H-H Kung
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
| | - S Maiti
- Department of Physics, University of Florida, Gainesville, Florida 32611, USA
| | - X Wang
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- Rutgers Center for Emergent Materials, Rutgers University, Piscataway, New Jersey 08854, USA
| | - S-W Cheong
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- Rutgers Center for Emergent Materials, Rutgers University, Piscataway, New Jersey 08854, USA
| | - D L Maslov
- Department of Physics, University of Florida, Gainesville, Florida 32611, USA
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
| | - G Blumberg
- Department of Physics & Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA
- National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia
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Nguyen TMH, Sandilands LJ, Sohn CH, Kim CH, Wysocki AL, Yang IS, Moon SJ, Ko JH, Yamaura J, Hiroi Z, Noh TW. Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd 2Os 2O 7. Nat Commun 2017; 8:251. [PMID: 28811471 PMCID: PMC5557926 DOI: 10.1038/s41467-017-00228-w] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Accepted: 06/12/2017] [Indexed: 11/17/2022] Open
Abstract
5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd2Os2O7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii-Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin-charge-lattice coupling and indicate that the metal-insulator transition in Cd2Os2O7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd2Os2O7 and that it exhibits complex spin-charge-lattice coupling.
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Affiliation(s)
- Thi Minh Hien Nguyen
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-742, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 151-742, Republic of Korea
| | - Luke J Sandilands
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-742, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 151-742, Republic of Korea
- Measurement Science and Standards, National Research Council of Canada, Ottawa, Ontario, Canada, K1A 0R6
| | - C H Sohn
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-742, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 151-742, Republic of Korea
| | - C H Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-742, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 151-742, Republic of Korea
| | | | - In-Sang Yang
- Department of Physics and Division of Nano-Sciences, Ewha Womans University, Seoul, 03760, Republic of Korea
| | - S J Moon
- Department of Physics, Hanyang University, Seoul, 04763, Republic of Korea
| | - Jae-Hyeon Ko
- Department of Physics, Hallym University, Chuncheon, Gangwondo, 24252, Republic of Korea
| | - J Yamaura
- Materials Research Center for Element Strategy, Tokyo Institute of Technology, Kanagawa, 226-8503, Japan
| | - Z Hiroi
- Institute for Solid State Physics, University of Tokyo, Kashiwa, 277-8581, Japan
| | - Tae Won Noh
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 151-742, Republic of Korea.
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 151-742, Republic of Korea.
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16
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Chu H, Zhao L, de la Torre A, Hogan T, Wilson SD, Hsieh D. A charge density wave-like instability in a doped spin-orbit-assisted weak Mott insulator. NATURE MATERIALS 2017; 16:200-203. [PMID: 28092687 DOI: 10.1038/nmat4836] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 11/21/2016] [Indexed: 06/06/2023]
Abstract
Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin-orbit coupled analogues of the parent state of cuprate high-temperature superconductors. Recent discoveries of pseudogap, magnetic multipolar ordered and possible d-wave superconducting phases in doped Sr2IrO4 have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates, no electronic instabilities have been reported in the doped bilayer iridate Sr3Ir2O7. Here we show that Sr3Ir2O7 realizes a weak Mott state with no cuprate analogue by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However, we detect a subtle charge density wave-like Fermi surface instability in metallic electron doped Sr3Ir2O7 at temperatures (TDW) close to 200 K via the coherent oscillations of its collective modes, which is reminiscent of that observed in cuprates. The absence of any signatures of a new spatial periodicity below TDW from diffraction, scanning tunnelling and photoemission based probes suggests an unconventional and possibly short-ranged nature of this density wave order.
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Affiliation(s)
- H Chu
- Department of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
| | - L Zhao
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - A de la Torre
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - T Hogan
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - S D Wilson
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - D Hsieh
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
- Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
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17
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Lu X, McNally DE, Moretti Sala M, Terzic J, Upton MH, Casa D, Ingold G, Cao G, Schmitt T. Doping Evolution of Magnetic Order and Magnetic Excitations in (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7}. PHYSICAL REVIEW LETTERS 2017; 118:027202. [PMID: 28128620 DOI: 10.1103/physrevlett.118.027202] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2016] [Indexed: 06/06/2023]
Abstract
We use resonant elastic and inelastic x-ray scattering at the Ir-L_{3} edge to study the doping-dependent magnetic order, magnetic excitations, and spin-orbit excitons in the electron-doped bilayer iridate (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} (0≤x≤0.065). With increasing doping x, the three-dimensional long range antiferromagnetic order is gradually suppressed and evolves into a three-dimensional short range order across the insulator-to-metal transition from x=0 to 0.05, followed by a transition to two-dimensional short range order between x=0.05 and 0.065. Because of the interactions between the J_{eff}=1/2 pseudospins and the emergent itinerant electrons, magnetic excitations undergo damping, anisotropic softening, and gap collapse, accompanied by weakly doping-dependent spin-orbit excitons. Therefore, we conclude that electron doping suppresses the magnetic anisotropy and interlayer couplings and drives (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} into a correlated metallic state with two-dimensional short range antiferromagnetic order. Strong antiferromagnetic fluctuations of the J_{eff}=1/2 moments persist deep in this correlated metallic state, with the magnon gap strongly suppressed.
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Affiliation(s)
- Xingye Lu
- Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - D E McNally
- Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Moretti Sala
- European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
| | - J Terzic
- Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
- Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - M H Upton
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - D Casa
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - G Ingold
- Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - G Cao
- Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
- Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - T Schmitt
- Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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18
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Gretarsson H, Sung NH, Porras J, Bertinshaw J, Dietl C, Bruin JAN, Bangura AF, Kim YK, Dinnebier R, Kim J, Al-Zein A, Moretti Sala M, Krisch M, Le Tacon M, Keimer B, Kim BJ. Persistent Paramagnons Deep in the Metallic Phase of Sr_{2-x}La_{x}IrO_{4}. PHYSICAL REVIEW LETTERS 2016; 117:107001. [PMID: 27636488 DOI: 10.1103/physrevlett.117.107001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Indexed: 06/06/2023]
Abstract
We have studied the magnetic excitations of electron-doped Sr_{2-x}La_{x}IrO_{4} (0≤x≤0.10) using resonant inelastic x-ray scattering at the Ir L_{3} edge. The long-range magnetic order is rapidly lost with increasing x, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1/2 Heisenberg model with exchange interactions whose spatial range increases with doping. We also find a doping-independent high-energy magnetic continuum, which is not described by this model. The spin-orbit excitons arising from the pseudospin-3/2 manifold of the Ir ions broaden substantially in the SRO phase, but remain largely separated from the low-energy magnons. Pseudospin-1/2 models are therefore a good starting point for the theoretical description of the low-energy magnetic dynamics of doped iridates.
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Affiliation(s)
- H Gretarsson
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - N H Sung
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - J Porras
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - J Bertinshaw
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - C Dietl
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - Jan A N Bruin
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - A F Bangura
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - Y K Kim
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Center for Correlated Electron Systems, Institute for Basic Science, Seoul 151-742, South Korea
- Department of Physics and Astronomy, Seoul National University, Seoul 151-747, South Korea
| | - R Dinnebier
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - Jungho Kim
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - A Al-Zein
- European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
| | - M Moretti Sala
- European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
| | - M Krisch
- European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
| | - M Le Tacon
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
- Karlsruher Institut für Technologie, Institut für Festkörperphysik, Hermann-v.-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
| | - B Keimer
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
| | - B J Kim
- Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany
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