Spin-Peierls Transition with Competing Interactions

Kuboki, Kazuhiro; Fukuyama, Hidetoshi

doi:10.1143/jpsj.56.3126

Cited by 104 publications

(77 citation statements)

References 18 publications

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“…1. In this sense our data are consistent with the large value of α needed to explain various experimental facts [11][12][13][14], and with the notion that the spin-Peierls transition in CuGeO 3 is driven by hard phonons [15][16][17].…”

Section: + δKsp)supporting

confidence: 90%

Excitations of the Field-Induced Quantum Soliton Lattice inCuGeO3

Enderle

Rønnow²,

McMorrow³

et al. 2001

Phys. Rev. Lett.

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Here we report the first inelastic neutron scattering study of the magnetic excitations in the incommensurate high-field phase of a spin-Peierls material. The results on CuGeO3 provide direct evidence for a finite excitation gap, two sharp magnetic excitation branches and a very low-lying excitation which is identified as a phason mode, the Goldstone mode of the incommensurate soliton lattice.A one-dimensional (1D) spin 1 2 Heisenberg antiferromagnet is unstable with respect to dimerization as well as long-range antiferromagnetic order. Coupled to a three-dimensional (3D) phonon field, it can undergo a second-order phase transition at a finite temperature into a dimerized (spin-Peierls) ground state with total spin S tot = i S i = 0 (D-phase). The dimerization is supported by antiferromagnetic next-nearest-neighbor exchange in the 1D chain direction. Antiferromagnetic (AF) interchain couplings prefer a Néel-type ground state and compete with dimerization.In the D-phase of a spin-Peierls material, the lowest magnetic excitation is an isolated triplet branch (S tot = 1). This excitation is a bound pair of domain walls with respect to the dimer order parameter. The two domain walls, or solitons, are created by breaking and delocalizing one dimer bond. The binding energy depends on the magnetic and elastic interchain interactions. The energy of the triplet is finite over the entire Brillouin zone and achieves its minima at wave vectors k = 0 and k = π c (the AF zone center, c being the average distance between two spins in the chain direction.) In a magnetic field, the S tot = 1 branch becomes Zeeman split, and a magnetized incommensurate (IC) phase is entered above a critical field H c , which corresponds approximately to the field where the lowest mode should soften to zero energy. In the IC-phase, the magnetization is generated by introducing more and more domain walls into the dimerized ground state. The unpaired spin at the center of a domain wall aligns parallel to the magnetic field (assumed to be to z). The transverse parts of the spin Hamiltonian, S + i S − j , delocalize the solitons. This results in an equal spacing of solitons, and thus leads to an IC superlattice of distortive and magnetic solitons. Their finite width implies a staggered magnetic polarization close to the soliton center.For a spin-Peierls system, the magnetic excitation spectrum in the IC-phase is expected to have finite excitation gaps, because at each given magnetic field the lattice, and hence the intrachain exchange, adapts to the magnetization and the number of solitons. Two excitation branches with polarization perpendicular to H are predicted, ∆ ± , corresponding to an increase or decrease of the total spin by 1, with minima at k = m CuGeO 3 is the first spin-Peierls compound where large single crystals are available [6], thus allowing the complete phonon and magnetic excitation spectra to be measured using neutron scattering techniques. The IC phase is also accessible, since magnetic fields up to 14.5 T have become available for...

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Section: + δKsp)supporting

confidence: 90%

Excitations of the Field-Induced Quantum Soliton Lattice inCuGeO3

Enderle

Rønnow²,

McMorrow³

et al. 2001

Phys. Rev. Lett.

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“…This can be confirmed by the bosonization technique in the following way. The effective Hamilton of the model of figure 3 in the continuum limit is written as [9,11,12,14,15] …”

Section: Analytical and Physical Approachmentioning

confidence: 99%

The ground state of anS= 1/2 distorted diamond chain - a model of Cu₃Cl₆(H₂O)₂·2H₈C₄SO₂

Okamoto¹,

Tonegawa²,

Takahashi³

et al. 1999

J. Phys.: Condens. Matter

110

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We study the ground state of the model Hamiltonian of the trimerized S = 1/2 quantum Heisenberg chain Cu3Cl6(H2O)22H8C4SO2 in which a non-magnetic ground state was observed recently. This model consists of stacked trimers and has three kinds of coupling constant describing the couplings between spins: the intra-trimer coupling constant J1 and the inter-trimer coupling constants J2 and J3. All of these constants are assumed to be antiferromagnetic. By use of an analytical method and physical considerations, we show that there are three phases on the 2 - 3 plane (2J2 / J1, 3J3 / J1): the dimer phase, the spin-fluid phase and the ferrimagnetic phase. The dimer phase is caused by the frustration effect. In the dimer phase, there exists an excitation gap between the twofold-degenerate ground state and the first excited state, which explains the non-magnetic ground state observed in Cu3Cl6(H2O)2·2H8C4SO2. We also obtain the phase diagram on the 2 - 3 plane from the numerical diagonalization data for finite systems by use of the Lanczos algorithm.

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“…The dimer phase of the J 1 -J 2 model has been a principal focus of theoretical and numerical studies. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Attention has recently shifted to multipolar, vector chiral and exotic phases of the model with J 1 < 0, an applied field or anisotropic exchange. [17][18][19][20][21][22][23] Sandvik 24 has reviewed numerical approaches to the HAF and related spin…”

Section: Introductionmentioning

confidence: 99%