Dynamics of Coupled Quantum Spin Chains

Schulz, H. J.

doi:10.1103/physrevlett.77.2790

Cited by 349 publications

(501 citation statements)

References 22 publications

(36 reference statements)

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“…61 Assuming the classical value for s ab = 0.25 at T → 0, one finds that the kinetic energy would come entirely from the high-spin optical excitations K 1 ͑ab͒ , while the low-spin excitations would be fully suppressed ͑Table III͒. Above T N the spin system is controlled by the dominating AF exchange constant J c , and s ab Ӎ 0.…”

Section: Optical Spectral Weights For Kcufmentioning

confidence: 99%

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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The temperature dependence and anisotropy of optical spectral weights associated with different multiplet transitions is determined by the spin and orbital correlations. To provide a systematic basis to exploit this close relationship between magnetism and optical spectra, we present and analyze the spin-orbital superexchange models for a series of representative orbital-degenerate transition metal oxides with different multiplet structure. For each case we derive the magnetic exchange constants, which determine the spin wave dispersions, as well as the partial optical sum rules. The magnetic and optical properties of early transition metal oxides with degenerate t 2g orbitals ͑titanates and vanadates with perovskite structure͒ are shown to depend only on two parameters, viz. the superexchange energy J and the ratio of Hund's exchange to the intraorbital Coulomb interaction, and on the actual orbital state. In e g systems important corrections follow from charge transfer excitations, and we show that KCuF 3 can be classified as a charge transfer insulator, while LaMnO 3 is a Mott insulator with moderate charge transfer contributions. In some cases orbital fluctuations are quenched and decoupling of spin and orbital degrees of freedom with static orbital order gives satisfactory results for the optical weights. On the example of cubic vanadates we describe a case where the full quantum spin-orbital physics must be considered. Thus information on optical excitations, their energies, temperature dependence, and anisotropy, combined with the results of magnetic neutron scattering experiments, provides an important consistency test of the spin-orbital models, and indicates whether orbital and/or spin fluctuations are important in a given compound. I. SUPEREXCHANGE AND OPTICAL EXCITATIONS AT ORBITAL DEGENERACYThe physical properties of Mott ͑or charge transfer͒ insulators are dominated by large on-site Coulomb interactions ϰU which suppress charge fluctuations. Quite generally, the Coulomb interactions lead then to strong electron correlations which frequently involve orbitally degenerate states, such as 3d ͑or 4d͒ states in transition metal compounds, and are responsible for quite complex behavior with often puzzling transport and magnetic properties. 1 The theoretical understanding of this class of compounds, with the colossal magnetoresistance ͑CMR͒ manganites as a prominent example, 2,3 has substantially advanced over the last decade, 4 after it became clear that orbital degrees of freedom play a crucial role in these materials and have to be treated on equal footing with the electron spins, which has led to a rapidly developing field, orbital physics. 5 Due to the strong onsite Coulomb repulsion, charge fluctuations in the undoped parent compounds are almost entirely suppressed, and an adequate description of these strongly correlated insulators appears possible in terms of superexchange. 6 At orbital degeneracy the superexchange interactions have a rather rich structure, represented by the so-called spin-orbita...

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Section: Optical Spectral Weights For Kcufmentioning

confidence: 99%

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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“…The low-temperature transition line to 3D ordering due to the small but finite interchain coupling J ′ can be calculated within an RPA approximation. The corresponding 3D susceptibility is then given by [1,20] …”

Section: Spin-1/heisenberg Chainsmentioning

confidence: 99%

“…Compounds of weakly coupled spin chains typically have an ordering transition from a high-temperature quasi-one-dimensional (1D) phase to a low-temperature threedimensional (3D) phase at a critical temperature which depends on the inter-chain coupling constant [1]. This transition can be suppressed if the individual chains are gapped spin liquids, as it is the case for Haldane or spin-Peierls systems, or for compounds with an Ising-anisotropy in the intra-chain exchange coupling.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Wessel

Haas

2000

Phys. Rev. B

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A theoretical description is presented for low-temperature magnetic-field induced threedimensional (3D) ordering transitions in strongly anisotropic quantum antiferromagnets, consisting of weakly coupled antiferromagnetic spin-1/2 chains and ladders. First, effective continuum field theories are derived for the one-dimensional subsystems. Then the Luttinger parameters, which determine the low-temperature susceptibilities of the chains and ladders, are calculated from the Bethe ansatz solution for these effective models. The 3D ordering transition line is obtained using a random phase approximation for the weak inter-chain (inter-ladder) coupling. Finally, considering a Ginzburg criterion, the fluctuation corrections to this approach are shown to be small. The nature of the 3D ordered phase resembles a Bose condensate of integer-spin magnons. It is proposed that for systems with higher spin degrees of freedom, e.g. N-leg spin-1/2 ladders, multi-component condensates can occur at high magnetic fields.

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“…In light of this, the proposal [5,6] that a novel longitudinal mode accompanies the crossover from 1D to 3D physics upon ordering in S=1/2 quasi-1D compounds is of great importance. In this letter we present a neutron scattering study of such a crossover in KCuF 3 and confirm the existence of this mode.…”

mentioning

confidence: 99%

Novel Longitudinal Mode in the Coupled Quantum Chain CompoundKCuF3

2000

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Inelastic neutron scattering measurements are reported that show a new longitudinal mode in the antiferromagnetically ordered phase of the spin-1/2 quasi-one-dimensional antiferromagnet KCuF 3 . This mode signals the cross-over from one-dimensional to three-dimensional behavior and indicates a reduction in the ordered spin moment of a spin-1/2 antiferromagnet. The measurements are compared with recent quantum field theory results and are found to be in excellent agreement. A feature of the data not predicted by theory is a damping of the mode by decay processes to the transverse spin-wave branches.

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Dynamics of Coupled Quantum Spin Chains

Cited by 349 publications

References 22 publications

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Three-dimensional ordering in weakly coupled antiferromagnetic ladders and chains

Novel Longitudinal Mode in the Coupled Quantum Chain CompoundKCuF3

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