Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory

Grüninger, M.; Windt, M.; Nunner, Tamara S.; Knetter, Christian; Schmidt, K. P.; Uhrig, Götz S.; Kopp, Thilo; Freimuth, A.; Ammerahl, U.; Büchner, B.; Revcolevschi, A.

doi:10.1016/s0022-3697(02)00251-2

Cited by 14 publications

(19 citation statements)

References 28 publications

(44 reference statements)

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“…We have measured the transmittance T of a polycrystalline sample that was compressed in a KBr pellet because K 4 Cu 4 OCl 10 is sensitive to moisture. Plotting − ln T yields an estimate of the absorption, as stated above [93]. The Cu-O bond-stretching mode is split into three distinct absorption peaks (see left panel of figure 20), indicating a distortion of the tetrahedra and a suppression of the magnetic quantum fluctuations.…”

Section: Y 2 Baniomentioning

confidence: 93%

“…Details concerning the crystal growth and characterization have been described in [86] for TiOCl, in [35,87] for RTiO 3 , in [88] for LaMnO 3 , in [89,90] Using a Fourier-transform spectrometer, we have measured the transmittance and reflectance in the energy range from 0.01 eV up to 3 eV at temperatures varying from 4 to 775 K. With the knowledge of both transmittance and reflectance, it is possible to directly calculate the complex optical conductivity σ(ω) [93]. For the transmittance measurements, the samples were polished on both sides.…”

Section: Methodsmentioning

confidence: 99%

“…Unfortunately, such a detailed analysis of neutron scattering data has failed so far due to the twinning of the samples [129]. Moreover, multiphonon Plotting − ln(T )/d, where T is the transmittance and d the sample thickness, yields an estimate of the absorption coefficient [93]. The curves have been shifted vertically for clarity.…”

Section: Orbitons Versus Multiphonon Peaks In Lamnomentioning

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: Y 2 Baniomentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Orbitons Versus Multiphonon Peaks In Lamnomentioning

confidence: 99%

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Optical study of orbital excitations in transition-metal oxides

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“…[23][24][25][26][27][28][29][30][31]9,10 In this mechanism, an absorbed photon simultaneously creates a Cu-O bond-stretching phonon and a multitriplet excitation with a singlet coupling. This simultaneous excitation enables us to probe a phononweighted sum of the Sϭ0 multitriplet excitation from the entire Brillouin zone.…”

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confidence: 99%

“…In fact, it was confirmed from the optical-conductivity measurements that the Sϭ0 two-triplet bound state exists below the two-triplet continuum in a S ϭ1/2 two-leg spin-ladder material (Ca,La) 14 Cu 24 O 41 . 31,9,10 In this paper, we investigate the optical-absorption spectra caused by the phonon-assisted two-triplet excitation in SrCu 2 O 3 two-leg spin-ladder systems on the basis of the pro-posed two minimal models. Using a continued fraction method based on the Lanczos algorithm, 32 we first calculate the wave-number-resolved Sϭ0 two-triplet excitation spectra.…”

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Optical absorption spectra inSrCu2O3two-leg spin ladder

Haga

Suga

2003

Phys. Rev. B

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We calculate the phonon-assisted optical-absorption spectra in SrCu 2 O 3 two-leg spin-ladder systems. The results for two models proposed for SrCu 2 O 3 are compared. In the model including the effects of a cyclic four-spin interaction, the shoulder structure appears at ϳ978 cm Ϫ1 and the peak appears at ϳ1975 cm Ϫ1 in the spectrum for polarization of the electric field parallel to the legs. In the other model which describes a pure two-leg ladder, the peak appears around the lower edge of the spectrum at ϳ1344 cm Ϫ1 . The feature can be effective in determining the proper model for SrCu 2 O 3 .

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The structure of operators in effective particle-conserving models

Knetter

Schmidt

Uhrig

2003

J. Phys. A: Math. Gen.

127

216

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For many-particle systems defined on lattices we investigate the global structure of effective Hamiltonians and observables obtained by means of a suitable basis transformation. We study transformations which lead to effective Hamiltonians conserving the number of excitations. The same transformation must be used to obtain effective observables.The analysis of the structure shows that effective operators give rise to a simple and intuitive perspective on the initial problem. The systematic calculation of n-particle irreducible quantities becomes possible constituting a significant progress. Details how to implement the approach perturbatively for a large class of systems are presented.

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Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory

Cited by 14 publications

References 28 publications

Optical study of orbital excitations in transition-metal oxides

Optical study of orbital excitations in transition-metal oxides

Optical absorption spectra inSrCu2O3two-leg spin ladder

The structure of operators in effective particle-conserving models

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