Optical Spectroscopy of Low-Dimensional Quantum Spin Systems

Grüninger, M.; Windt, M.; Benckiser, E.; Nunner, Tamara S.; Schmidt, K. P.; Uhrig, Götz S.; Kopp, Thilo

doi:10.1007/978-3-540-44838-9_7

Cited by 6 publications

(16 citation statements)

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“…Considering a transition-metal site with inversion symmetry, the above matrix element vanishes due to the even parity of the 3d wave functions, even|odd|even = 0. 8 Parts of the data on LaMnO 3 and on CaCu 2 O 3 have been reported before in [51,63].…”

Section: The Case Of a Single Ionmentioning

confidence: 85%

“…Lorenzana-Sawatzky-type phonon-assisted magnetic excitations were observed at about 0.4 eV [63]. The onset of excitations across the charge-transfer gap is observed at about 1.2-1.3 eV.…”

Section: Y 2 Baniomentioning

confidence: 92%

“…The crystal structure of CaCu 2 O 3 shows buckled Cu 2 O 3 layers which are stacked along the c direction [150] (see figure 16). Magnetically, the system is strongly anisotropic, with a dominant antiferromagnetic coupling between the Cu spins parallel to the b axis, and weak couplings in the perpendicular directions (J b J a ≈ J c ) [63,151]. The weak 3D coupling gives rise to long-range order below T N ≈ 25 K. The interlayer distance amounts to 3.7 Å, and the local environment of the 3d 9 Cu 2+ ions is close to a square of four O ions.…”

Section: Y 2 Baniomentioning

confidence: 99%

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Optical study of orbital excitations in transition-metal oxides

et al. 2005

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Collective orbital excitations in orbitally ordered YVO3 and HoVO3 E Benckiser, R Rückamp, T Möller et al. Abstract. The orbital excitations of a series of transition-metal compounds are studied by means of optical spectroscopy. Our aim was to identify signatures of collective orbital excitations by comparison with experimental and theoretical results for predominantly local crystal-field excitations. To this end, we have studied TiOCl, RTiO 3 (R = La, Sm and Y), LaMnO 3 , Y 2 BaNiO 5 , CaCu 2 O 3 and K 4 Cu 4 OCl 10 , ranging from early to late transition-metal ions, from t 2g to e g systems, and including systems in which the exchange coupling is predominantly three-dimensional, one-dimensional or zero-dimensional. With the exception of LaMnO 3 , we find orbital excitations in all compounds. We discuss the competition between orbital fluctuations (for dominant exchange coupling) and crystal-field splitting (for dominant coupling to the lattice). Comparison of our experimental results with configuration-interaction cluster calculations in general yields good agreement, demonstrating that the coupling to the lattice is important for a 7 Author to whom any correspondence should be addressed. quantitative description of the orbital excitations in these compounds. However, detailed theoretical predictions for the contribution of collective orbital modes to the optical conductivity (e.g. the line shape or the polarization dependence) are required to decide on a possible contribution of orbital fluctuations at low energies, in particular, in case of the orbital excitations at ≈0.25 eV in RTiO 3 . Further calculations are called for which take into account the exchange interactions between the orbitals and the coupling to the lattice on an equal footing. Contents

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Section: The Case Of a Single Ionmentioning

confidence: 85%

“…Lorenzana-Sawatzky-type phonon-assisted magnetic excitations were observed at about 0.4 eV [63]. The onset of excitations across the charge-transfer gap is observed at about 1.2-1.3 eV.…”

Section: Y 2 Baniomentioning

confidence: 92%

Section: Y 2 Baniomentioning

confidence: 99%

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Optical study of orbital excitations in transition-metal oxides

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“…This was also found in treatments for the two-dimensional square lattice 18,43,45 . However, the complete magnetic infrared absorption spectrum (including the high-energy part) of La6Ca8 can be described quantitatively by including multi-particle contributions 27,28 . Here x cyc does not play the dominant role for the high-energy spectral weight 80 .…”

Section: High-energy Spectral Weightmentioning

confidence: 99%

“…Besides the usual Heisenberg exchange terms the minimal magnetic model includes four-spin interactions which are 4-5 times smaller than the leading Heisenberg couplings 19,27,28,32,33 . The existence and the size of the four-spin interactions are consistent with theoretical derivations of generalized t-J models from one-band or three-band Hubbard models 34,35,36,37,38,39,40 .…”

Section: Introductionmentioning

confidence: 99%

Raman response of magnetic excitations in cuprate ladders and planes

et al. 2005

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An unified picture for the Raman response of magnetic excitations in cuprate spin-ladder compounds is obtained by comparing calculated two-triplon Raman line-shapes with those of the prototypical compounds SrCu2O3 (Sr123), Sr14Cu24O41 (Sr14), and La6Ca8Cu24O41 (La6Ca8). The theoretical model for the two-leg ladder contains Heisenberg exchange couplings J and J ⊥ plus an additional four-spin interaction Jcyc. Within this model Sr123 and Sr14 can be described by x := J /J ⊥ = 1.5, xcyc := Jcyc/J ⊥ = 0.2, J Sr123 ⊥ = 1130 cm −1 and J Sr14 ⊥ = 1080 cm −1 . The couplings found for La6Ca8 are x = 1.2, xcyc = 0.2, and J La6Ca8 ⊥ = 1130 cm −1 . The unexpected sharp two-triplon peak in the ladder materials compared to the undoped two-dimensional cuprates can be traced back to the anisotropy of the magnetic exchange in rung and leg direction. With the results obtained for the isotropic ladder we calculate the Raman line-shape of a two-dimensional square lattice using a toy model consisting of a vertical and a horizontal ladder. A direct comparison of these results with Raman experiments for the two-dimensional cuprates R2CuO4 (R=La,Nd), Sr2CuO2Cl2, and YBa2Cu3O 6+δ yields a good agreement for the dominating two-triplon peak. We conclude that short range quantum fluctuations are dominating the magnetic Raman response in both, ladders and planes. We discuss possible scenarios responsible for the high-energy spectral weight of the Raman line-shape, i.e. phonons, the triple-resonance and multi-particle contributions.

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Multiple spin-orbit excitons and the electronic structure of α−RuCl3

Warzanowski

Borgwardt

Hopfer

et al. 2020

Phys. Rev. Research

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The honeycomb compound α-RuCl 3 is widely discussed as a proximate Kitaev spin-liquid material. This scenario builds on spin-orbit entangled j = 1/2 moments arising for a t 5 2g electron configuration with strong spin-orbit coupling λ and a large cubic crystal field. The actual low-energy electronic structure of α-RuCl 3 , however, is still puzzling. In particular, infrared absorption features at 0.30, 0.53, and 0.75 eV seem to be at odds with a j = 1/2 scenario. Also the energy of the spin-orbit exciton, the excitation from j = 1/2 to 3/2, and thus the value of λ, are controversial. Combining infrared and Raman data, we show that the infrared features can be attributed to single, double, and triple spin-orbit excitons. We find λ = 0.16 eV and = 42(4) meV for the observed noncubic crystal-field splitting, supporting the validity of the j = 1/2 picture for α-RuCl 3. The unusual strength of the double excitation is related to the underlying hopping interactions, which form the basis for dominant Kitaev exchange.

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Optical Spectroscopy of Low-Dimensional Quantum Spin Systems

Cited by 6 publications

References 0 publications

Optical study of orbital excitations in transition-metal oxides

Optical study of orbital excitations in transition-metal oxides

Raman response of magnetic excitations in cuprate ladders and planes

Multiple spin-orbit excitons and the electronic structure of α−RuCl3

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