Ordered phases in spin-Peierls systems

Uhrig, Götz S.

doi:10.1016/s0921-4526(99)01703-2

Physica B: Condensed Matter

2000

DOI: 10.1016/s0921-4526(99)01703-2

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Ordered phases in spin-Peierls systems

Götz S. Uhrig

Abstract: The microscopic description of spin-Peierls substances is discussed. Particular attention is paid to the ordered (dimerised and incommensurably modulated) phases. Important points are the adiabatic and the antiadiabatic approach, generic soliton forms, elastic and magnetic interchain couplings. The wealth and the accuracy of experimental information collected for the first inorganic spin-Peierls substance CuGeO3 motivates this work.

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Cited by 4 publications

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“…It has been recently noted [19,20] that a full selfconsistent treatment (where < φ 2 > in Eq. 5 is not fixed to its value in the ground state) changes the form of the soliton.…”

mentioning

confidence: 99%

Mixing of magnetic and phononic excitations in incommensurate spin-Peierls systems

Dobry

Ibaceta

2001

Phys. Rev. B

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We analyze the excitation spectra of a spin-phonon coupled chain in the presence of a soliton. This is taken as a microscopic model of a Spin-Peierls material placed in a high magnetic field. We show, by using a semiclassical approximation in the bosonized representation of the spins that a trapped magnetic state obtained in the adiabatic approximation is destroyed by dynamical phonons. Low energy states are phonons trapped by the soliton. When the magnetic gap is smaller than the phonon frequencies the only low energy state is a mixed magneto-phonon state with the energy of the gap. We emphasize that our results are relevant for the Raman spectra of the inorganic Spin-Peierls material CuGeO3.The discovery in 1993 by Hase et al [1] of the first inorganic Spin-Peierls compound CuGeO 3 has opened the possibility of study the physics of this collective phenomena in a deep way. Several experimental proves have given an exhaustive information about the excitation spectra of this system and its evolution with an applied magnetic field. The effect of non-magnetic impurities has been investigated also.Theoretical studies have focused on simplified magnetic model. The excitation spectra in the low temperature phase have been analyzed using a dimerized and frustrated Heisenberg chain as a minimal model for this material [3][4][5]. The logic underlying these studies are: the competition between magnetic and elastic energies resolves in the low temperature phase in the dimerization of the lattice. Once this process takes place, phononic and magnetic excitation completely decouple and the magnetic excitations are the same as the chemical dimerized system. This point of view is based on an adiabatic approximation supposing that the energy scale of the magnetic process are high enough respect to the phononic ones. As it has been recently emphasized [6], this relation is not fulfilled for CuGeO 3 where the phonons relevant for the dimerization process are about one order of magnitude more energetic than the magnetic gap. The adiabatic approximation is questionable for this system. An antiadiabatic approach has been developed. The frustrated interaction arises, in this context, from the integration of the in-chain phonons and the explicit dimerization from the interchain interaction treated in a mean field approximation [7]. The same frustrated-dimerized Hamiltonian is therefore obtained but with a reinterpretation of the parameters. What is clearly missed in these studies is a general understanding on how spin and phonons mix as elementary excitation and how the spectra of Spin-Peierls systems is built as a result of this mixing. Some recent numerical results have partially addressed this question [8].In this paper, we analyze the excitation spectra of onedimensional spin-phonon system by semiclassical techniques on the bosonized representation of the spins subsystem. We focus on the properties of this system in a high magnetic field. In the dimerized phase the system is in a singlet ground state. Coupling with a magnetic field...

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“…It has been recently noted [19,20] that a full selfconsistent treatment (where < φ 2 > in Eq. 5 is not fixed to its value in the ground state) changes the form of the soliton.…”

mentioning

confidence: 99%

Mixing of magnetic and phononic excitations in incommensurate spin-Peierls systems

Dobry

Ibaceta

2001

Phys. Rev. B

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Field theoretical study of a spin-1/2 ladder with unequal chain exchanges

Sarkar

Sen²

2002

Phys. Rev. B

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We study the low-energy properties of a Heisenberg spin-1/2 zigzag ladder with different exchange constants on the two chains. Using a nonlinear σ-model field theory and abelian bosonization, we find that the excitations are gapless, with a finite spin wave velocity, if the values of the chain exchanges are small. If the chain exchanges are large, the system is gapped, and the energy spectra of the kink and antikink excitations are different from each other.

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X-ray scattering study of the incommensurate phase in Mg-dopedCuGeO3

et al. 2002

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Ordered phases in spin-Peierls systems

Cited by 4 publications

References 44 publications

Mixing of magnetic and phononic excitations in incommensurate spin-Peierls systems

Mixing of magnetic and phononic excitations in incommensurate spin-Peierls systems

Field theoretical study of a spin-1/2 ladder with unequal chain exchanges

X-ray scattering study of the incommensurate phase in Mg-dopedCuGeO3

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