Soliton lattices in the incommensurate spin-Peierls phase: Local distortions and magnetizations

Uhrig, Götz S.; Schönfeld, Friedhelm; Boucher, Jean‐Philippe; Horvatić, M.

doi:10.1103/physrevb.60.9468

Cited by 25 publications

(42 citation statements)

References 42 publications

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“…A pinning to impurities would create a disordered soliton lattice, in contradiction to our earlier structural study [7]. The discreteness of the lattice leads to a phason pinning energy of the order 0.003 meV [3], which is much too small. However, this estimate neglects interchain couplings, and does not take into account the non-sinusoidal magnetic modulation [7], both of which may enhance the phason gap in CuGeO 3 .…”

Section: + δKsp)contrasting

confidence: 81%

See 1 more Smart Citation

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)contrasting

confidence: 81%

“…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 . The precise value and field dependences of the modes ∆ ± and ∆ 0 depend on the details of the assumptions used in the models [2][3][4][5].…”

mentioning

confidence: 99%

Excitations of the Field-Induced Quantum Soliton Lattice inCuGeO3

Enderle

Rønnow²,

McMorrow³

et al. 2001

Phys. Rev. Lett.

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show abstract

“…Laukamp, et al have also studied the open chain problem by a Monte Carlo method and a DMRG method [3]. Magnetic structures at edges cause interesting effects on the NMR line shape [4,5]. In particular, the observation [4] of a broad background in the NMR spectrum in Sr 2 CuO 3 has been found to agree with the features predicted by the theoretical work on the field-induced local staggered magnetization [2].…”

Section: Introductionmentioning

confidence: 69%

Local magnetic structure due to inhomogeneity of interaction inS=12antiferromagnetic chains

et al. 2000

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We study the magnetic properties of S = 1/2 antiferromagnetic Heisenberg chains with inhomogeneity of interaction. Using a quantum Monte Carlo method and an exact diagonalization method, we study bond-impurity effect in the uniform S = 1/2 chain and also in the bond-alternating chain. Here 'bond impurity' means a bond with strength different from those in the bulk or a defect in the alternating order. Local magnetic structures induced by bond impurities are investigated both in the ground state and at finite temperatures, calculating the local magnetization, the local susceptibility and the local field susceptibility. We also investigate the force acting between bond impurities and find the force generally attractive.

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“…After the existence of the incommensurate modulation is established, the subsequent interest on this I phase is how the spin and lattice modulation evolves under higher magnetic fields (well above H c ), where the soliton distance becomes comparable to the soliton width. [7][8][9] The discovery of the inorganic SP compound CuGeO 3 (Ref. 10) opened the way to impurity substitiution and it turned out that just a small amount of the impurity modifies the phase diagram to a more complicated one; 11,12 with decreasing temperature, after the appearance of D phase at T SP , the system shows another transition to a peculiar ordered phase, where antiferromagnetic (AF) long-range order and the SP order coexist [dimerized AF (D-AF) phase].…”

Section: Introductionmentioning

confidence: 99%

Thermal conductivity of pure and Mg-dopedCuGeO3in the incommensurate phase

et al. 2001

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The thermal conductivity κ of Cu1−xMgxGeO3 is measured in magnetic fields up to 16 T. At the transition field Hc to the high-field incommensurate (I) phase, κ abruptly decreases. While κ of the pure CuGeO3 is enhanced with the application of higher magnetic fields, an anomalous plateau feature shows up in the κ(H) profile in the I phase of the Mg-doped samples which includes antiferromagnetic ordering (I-AF phase). With the help of specific heat data, taken supplementally for the identical samples, the above features are well understood that phonons are strongly scattered by spin solitons and that κ in the I phase is governed by their spatial distribution. In particular, the plateau feature in the doped samples suggests "freezing" of the solitons, in which antiferromagnetism must be playing an essential role because this feature is absent at temperatures above TN .

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Soliton lattices in the incommensurate spin-Peierls phase: Local distortions and magnetizations

Cited by 25 publications

References 42 publications

Excitations of the Field-Induced Quantum Soliton Lattice inCuGeO3

Excitations of the Field-Induced Quantum Soliton Lattice inCuGeO3

Local magnetic structure due to inhomogeneity of interaction inS=12antiferromagnetic chains

Thermal conductivity of pure and Mg-dopedCuGeO3in the incommensurate phase

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