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Knöll, P.; Thomsen, C.; Cardona, M.; Murugaraj, P.

doi:10.1103/physrevb.42.4842

Cited by 95 publications

(80 citation statements)

References 18 publications

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“…Therefore, other processes must contribute which are not described by the Heisenberg model with ring exchange alone. It was proposed, that the damping due to spin-phonon coupling [14,15,16] is responsible for the peak width which in the current calculation is underestimated by roughly a factor 2. In order to incorporate extrinsic sources for damping beyond the extended Heisenberg Hamiltonian Eq.…”

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confidence: 58%

“…The results of these studies led to a peak position and a two-magnon lineshape which were very close to the spin-wave results. Furthermore, the value of the exchange integral J = 1440K for La 2 CuO 4 as extracted from the position of the twomagnon Raman peak appears too small in comparison to early neutron scattering results for the spin-wave spectrum (J = 1650K), see Ref.[13] and references therein.The asymmetric lineshape of the two-magnon Raman intensity [3] has led to proposals that spin-phonon interactions [14,15,16], resonant phenomena [17,18], purely fermionic contributions [19], or cyclic ring exchange [20,21,22] need to be included beyond the nn Heisenberg model. A possible importance of ring exchange for Raman scattering was conjectured also from numerical calculations [23] which showed that a finite J ✷ gives rise to additional high energy contributions in the Raman intensity -yet with little spectral weight.…”

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Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Катанин

Kampf

2003

Phys. Rev. B

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We evaluate the Raman light scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange J✷. With the exchange couplings as fixed before from an accurate fit to the spin wave dispersion in La2CuO4, leading in particular to J✷ = 0.24J, we demonstrate in a parameter free calculation that the inclusion of the plaquette exchange contribution to the dispersion and the magnon-magnon interaction vertex gives a peak position in B1g scattering geometry Emax = 2.71J which is in excellent agreement with the experimental data. Yet, the intrinsic width and the lineshape of the two-magnon remain beyond a descriptions in terms of a spin-only Hamiltonian.PACS Numbers: 75.40.Gb, 75.10.Jm, 76.60.Es The magnetic properties of La 2 CuO 4 have been the subject of many detailed investigations over the last decade. Understanding this undoped parent compound of high temperature superconducting cuprates is a precondition for the many theories which describe metallic cuprates by doping carriers into a layered antiferromagnet. The conventional starting point for undoped cuprates is the two-dimensional (2D) spin-1/2 Heisenberg model with nearest-neighbor (nn) exchange interaction J [1]. Despite the substantial progress on the theory of the 2D Heisenberg antiferromagnet [2], some of the experimental facts for La 2 CuO 4 have clearly demonstrated that a complete description of the magnetic excitations requires additional physics not contained in the 2D Heisenberg model with J only. Examples include the asymmetric lineshape of the two-magnon Raman intensity [3] or the infrared optical absorption [4].The importance of an additional ring (plaquette) exchange coupling for La 2 CuO 4 recently found direct experimental support from the observed dispersion of the spin-waves along the magnetic Brillouin zone boundary [5]. A fit of the experimental results [5] using the theoretical spin-wave dispersion, which consistently includes quantum renormalization effects [6], has provided accurate values for the nn exchange integral J = 1720K and the ring-exchange coupling J ✷ = 0.24J. The new estimate for J corrects previous values which have been used in past years and which were consistently 10 to 15% lower. Also the value for J ✷ must be considered surprisingly large, but the spin stiffness and the Néel temperature calculated with the new parameter set obtained in Ref. [6] were in excellent agreement with the experimental data and thereby confirmed the deduced exchange coupling parameters. The value of the ring exchange J ✷ also agreed with the strong-coupling expansion studies of the three-band Hubbard model in the parameter range relevant for CuO 2 planes [7].The Heisenberg model with J only was previously found insufficient to describe the experimentally observed asymmetry and width of the Raman spectra of undoped cuprate compounds [3]. The Raman spectrum of the Heisenberg model was investigated within the ladder approximation for the magnon-magnon scattering vertex many years ago [8,9] and gave an almost symme...

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Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Катанин

Kampf

2003

Phys. Rev. B

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“…These observations indicate an additional damping channel arising from coupling to a different set of excitations. Potential candidates include charge excitations across the small Mott gap, spin-orbit excitons, [13] and phonons [33] Fig. 2(a) and (c), the latter modes display a pronounced Fano asymmetry at high-temperature (T > T N ) which vanishes for T < T N .…”

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confidence: 99%

Two-Magnon Raman Scattering and Pseudospin-Lattice Interactions inSr2IrO4andSr3Ir2O<

et al. 2016

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We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, lineshapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the lineshapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.PACS numbers: 71.70. Ej, 75.25.Dk, 75.47.Lx, The recent discovery of Mott-insulating states driven by the confluence of intra-atomic spin-orbit coupling and electronic correlations ("spin-orbit Mott insulators") has triggered a wave of research on novel magnetic ground states and excitations. The most widely studied spinorbit Mott insulators are iridium oxides based on Ir 4+ions with electron configuration 5d 5 and total angular momentum j eff = 1 2 . Mott-insulating iridates with j effpseudospins arranged on geometrically frustrated lattices are promising candidates for spin-liquid states with unusual transport properties and fractionalized excitations. [1][2][3][4][5] Iridates with square-lattice geometries, on the other hand, have been extensively investigated as possible analogues of the cuprate high-temperature superconductors whose low-energy excitations are characterized by the pure spin quantum number S = 1 2 . Indeed, resonant inelastic x-ray scattering (RIXS) experiments [6] have shown that the magnon excitations of the prototypical square-lattice antiferromagnet Sr 2 IrO 4 are well described by the Heisenberg model, in close analogy to those of the isostructural Mott-insulator La 2 CuO 4 . Very recently, experiments on doped Sr 2 IrO 4 have uncovered tantalizing evidence of a Fermi surface split up into disjointed segments ("Fermi arcs") [7] and a lowtemperature gap with d-wave symmetry [8,9], which are hallmarks of the doped cuprates. [10] This rapidly advancing research frontier has raised fundamental questions about the microscopic electronic structure of spin-orbit Mott insulators. A particularly important question concerns the orbital degeneracy, which plays a central role in the phase behavior of 3d-electron materials, where the spin-orbit coupling is negligible. In the widely studied manganates, for instance, the orbital degeneracy of the manganese ions is only partially lifted by crystalline electric fields, and coupling of low-lying orbital excitations to lattice distortions leads to the formation of polarons which dominate the physical properties of the doped manganates. In Mottinsulating cuprates, on the other hand, the S = 1 2 moments of the orbitally non-degenerate Cu 2+ ions do not couple significantly to the crystal lattice, so that spin...

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“…We propose that a major shift may result from coupling to phonons: It was shown that the unexpected large width ∆E B 1g of the Raman peak may be explained by such a coupling which is effective only for zone boundary magnons [24,25]. This mechanism may be responsible for a shift of the B 1g Raman peak of the order of (∆E B 1g /E B 1g ) 2 but will effect the absorption peaks of Fig.…”

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Spin-waves in the mid-infrared spectrum of antiferromagnetic YBa ₂ Cu ₃ O _6.0

Grüninger¹,

Münzel²,

Gaymann³

et al. 1996

Europhys. Lett.

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The mid-infrared spin-wave spectrum of antiferromagnetic YBa 2 Cu 3 O 6.0 was determined by infrared transmission and reflection measurements (k c) at T = 10 K. Excitation of single magnons of the optical branch was observed at E op = 178.0 meV. Two further peaks at 346 meV (≈ 1.94 E op ) and 470 meV (≈ 2.6 E op ) both belong to the two-magnon spectrum. Linear spin wave theory is in good agreement with the measured two-magnon spectrum, and allows to determine the exchange constant J to be about 120 meV, whereas the intrabilayer coupling J 12 is approximately 0.55 J. 74.25.Gz, 74.25.Ha, 75.30.Ds High temperature superconductors are basically layered copper-oxide materials. It is widely accepted that the relevant electronic degrees of freedom are confined to copper-oxide planes. The number of CuO 2 planes per unit cell varies: e.g., La 2−x Sr x CuO 4 exists in a single plane form with a large spacing between planes of ≈ 13.2Å, and YBa 2 Cu 3 O 6+x has a double layer structure with intra-and interbilayer spacings of ≈ 3.3Å and 8.5Å, respectively. Electronic correlations, and hence spin dynamics [1], may depend on the type of stacking of the planes. More specifically, a sizable coupling J 12 between spins on adjacent planes of a bilayer will influence the spin excitation spectrum as well as the nature of the ground state. This may have been seen already in doped compounds: the normal state spin susceptibility of La 2−x Sr x CuO 4 extrapolates to a finite value at zero temperature, whereas it extrapolates to zero for YBa 2 Cu 3 O 6.6 [2]. This may be interpreted as a signature for the opening of a spin excitation gap in YBa 2 Cu 3 O 6.6 at low temperatures [3]-a behavior certainly not encountered in Fermi liquids. Further, a spin density wave ordering for La 2−x Sr x CuO 4 has been proposed, but for YBa 2 Cu 3 O 6.6 a singlet pairing of spins in adjacent CuO 2 planes with strong antiferromagnetic fluctuations within a plane [4,2,5]. Such a scenario seems to require an unrealistically large J 12 2.5J [6], where J is the in-plane exchange coupling of the Heisenberg Hamiltonian supposed to describe the low energy spin dynamics of a single bilayer for zero doping (x = 0). However it was argued that, for finite doping, the itinerant carriers destroy the antiferromagnetism of the insulating phase and, therefore, much smaller values of J 12 will produce a singlet interplane pairing in the conducting phase of YBa 2 Cu 3 O 6.6 . 74Up to now, no experimental evidence has been given of a sizable bilayer coupling (J 12 ∼ J). In neutron-scattering experiments on YBa 2 Cu 3 O 6+x , the in-plane coupling was determined from the dispersion of acoustic spin-waves and was found to be extremely large (J = 120 ± 20 meV [7], J = 150 meV [8], both for x = 0.15). Yet, no optical modes have been found for energies up to 60 meV [7,9], suggesting a bilayer coupling of J 12 8 meV. In Raman-1

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Temperature-dependent lifetime of spin excitations inRBa2Cu3

Cited by 95 publications

References 18 publications

Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Two-Magnon Raman Scattering and Pseudospin-Lattice Interactions inSr2IrO4andSr3Ir2O<

Spin-waves in the mid-infrared spectrum of antiferromagnetic YBa ₂ Cu ₃ O _6.0

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Temperature-dependent lifetime of spin excitations inRBa2Cu3

Cited by 95 publications

References 18 publications

Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Theoretical analysis of magnetic Raman scattering inLa2CuO4:Two-magnon intensity with the inclusion of ring exchange

Two-Magnon Raman Scattering and Pseudospin-Lattice Interactions inSr2IrO4andSr3Ir2O<

Spin-waves in the mid-infrared spectrum of antiferromagnetic YBa 2 Cu 3 O 6.0

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Spin-waves in the mid-infrared spectrum of antiferromagnetic YBa ₂ Cu ₃ O _6.0