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1.
We consider a spin-1/2 tube (a three-leg ladder with periodic boundary conditions) with a Hamiltonian given by two projection operators-one on the triangles and the other on the square plaquettes on the side of the tube-that can be written in terms of Heisenberg and four-spin ring exchange interactions. We identify 3 phases: (i)?for strongly antiferromagnetic exchange on the triangles, an exact ground state with a gapped spectrum can be given as an alternation of spin and chirality singlet bonds between nearest triangles; (ii)?for ferromagnetic exchange on the triangles, we recover the phase of the spin-3/2 Heisenberg chain; (iii)?between these two phases, a gapless incommensurate phase exists. We construct an exact ground state with two deconfined domain walls and a gapless excitation spectrum at the quantum phase transition point between the incommensurate and dimerized phases. 相似文献
2.
We investigate the phase diagram of antiferromagnetic spin ladders with additional exchange interactions on diagonal bonds by variational and numerical methods. These generalized spin ladders interpolate smoothly between the [Formula: see text] chain with competing nn and nnn interactions, the [Formula: see text] chain with alternating exchange and the antiferromagnetic (AF) S = 1 chain. The Majumdar - Ghosh ground states are formulated as matrix product states and are shown to exhibit the same type of hidden order as the AF S = 1 chain. Generalized matrix product states are used for a variational calculation of the ground state energy and the spin and string correlation functions. Numerical (Lanczos) calculations of the energies of the ground state and of the low-lying excited states are performed, and compare reasonably with the variational approach. Our results support the hypothesis that the dimer and Majumdar - Ghosh points are in the same phase as the AF S = 1 chain. 相似文献
3.
We show that Dzyaloshinskii-Moriya (DM) interactions can substantially modify the phase diagram of spin-1/2 Heisenberg ladders in a magnetic field provided they compete with exchange. For nonfrustrated ladders, they induce a local magnetization along the DM vector that turns the gapless intermediate phase into an Ising phase with broken translational symmetry, while for frustrated ladders, they extend the Ising order of the half-integer plateau to the surrounding gapless phases of the purely Heisenberg case. Implications for experimental ladder and dimer systems are discussed. 相似文献
4.
S. Nemati S. Batebi S. Mahdavifar 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(3):329-335
We consider isotropic spin-1/2 two-leg ladders with dominant spatially-modulated rung
exchanges. We study the effect of a uniform magnetic field on the ground state phase
diagram of the model using perturbation theory and the numerical Lanczos method. The
ground state phase diagram consists of two gapless Luttinger liquid (LL) and three gapped
phases. Numerically, we calculate the concurrence between two spins and the entanglement
entropy between legs. Numerical experiment shows that the gapless LL phases are
fundamentally different. In the first LL phase, only spins on rungs are entangled, but in
the second LL phase the spins on legs are long-distance entangled. Therefore, the
concurrence between spins on legs can be considered as a function to distinguish the LL
phases. 相似文献
5.
Helton JS Chen Y Bychkov GL Barilo SN Rogado N Cava RJ Lynn JW 《J Phys Condens Matter》2012,24(1):016003
Single crystal neutron diffraction studies have been performed on the S = 3/2 kagome staircase compound Co(3)V(2)O(8) with a magnetic field applied along the magnetization easy-axis ([Formula: see text]). Previous zero-field measurements (Chen Y et al 2006 Phys. Rev. B 74 014430) reported a rich variety of magnetic phases, with a ferromagnetic ground state as well as incommensurate, transversely polarized spin density wave (SDW) phases (with a propagation vector of [Formula: see text]) interspersed with multiple commensurate lock-in transitions. The magnetic phase diagram with [Formula: see text] adds further complexity. For small applied fields, μ(0)H ≈ 0.05 T, the commensurate lock-in phases are destabilized in favor of the incommensurate SDW ones, while slightly larger applied fields restore the commensurate lock-in phase with δ = 1/2 and yield a new commensurate phase with δ = 2/5. For measurements in an applied field, higher-order scattering is observed that corresponds to the second harmonic. 相似文献
6.
G. I. Japaridze S. Mahdavifar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):59-66
The ground-state magnetic phase diagram of a spin S=1/2 two-leg ladder with alternating rung exchange J⊥(n)=J⊥[1 + (-1)n δ] is studied using the analytical and numerical approaches. In the limit where the rung exchange is dominant, we have mapped
the model onto the effective quantum sine-Gordon model with topological term and identified two quantum phase transitions
at magnetization equal to the half of saturation value from a gapped to the gapless regime. These quantum transitions belong
to the universality class of the commensurate-incommensurate phase transition. We have also shown that the magnetization curve
of the system exhibits a plateau at magnetization equal to the half of the saturation value. We also present a detailed numerical
analysis of the low energy excitation spectrum and the ground state magnetic phase diagram of the ladder with rung-exchange
alternation using Lanczos method of numerical diagonalizations for ladders with number of sites up to N = 28. We have calculated
numerically the magnetic field dependence of the low-energy excitation spectrum, magnetization and the on-rung spin-spin correlation
function. We have also calculated the width of the magnetization plateau and show that it scales as δν, where critical exponent varies from ν = 0.87±0.01 in the case of a ladder with isotropic antiferromagnetic legs to ν = 1.82±0.01
in the case of ladder with ferromagnetic legs. Obtained numerical results are in an complete agreement with estimations made
within the continuum-limit approach. 相似文献
7.
P. N. Timonin 《Journal of Experimental and Theoretical Physics》2016,122(6):1052-1059
Gapless phases in ground states of low-dimensional quantum spin systems are rather ubiquitous. Their peculiarity is a remarkable sensitivity to external perturbations due to permanent criticality of such phases manifested by a slow (power-low) decay of pair correlations and the divergence of the corresponding susceptibility. A strong influence of various defects on the properties of the system in such a phase can then be expected. Here, we consider the influence of vacancies on the thermodynamics of the simplest quantum model with a gapless phase, the isotropic spin-1/2 XX chain. The existence of the exact solution of this model gives a unique opportunity to describe in detail the dramatic effect of dilution on the gapless phase—the appearance of an infinite series of quantum phase transitions resulting from level crossing under the variation of a longitudinal magnetic field. We calculate the jumps in the field dependences of the ground-state longitudinal magnetization, susceptibility, entropy, and specific heat appearing at these transitions and show that they result in a highly nonlinear temperature dependence of these parameters at low T. Also, the effect of enhancement of the magnetization and longitudinal correlations in the dilute chain is established. The changes of the pair spin correlators under dilution are also analyzed. The universality of the mechanism of the quantum transition generation suggests that similar effects of dilution can also be expected in gapless phases of other low-dimensional quantum spin systems. 相似文献
8.
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal disorder is determined using quantum Monte Carlo simulations. A sequence of quantum glass phases intervene at the interface between the Mott insulating and the superfluid phases of the clean system. In addition to the standard Bose glass phase, the coexistence of gapless and gapped regions close to the Mott insulating phase leads to a novel Mott glass regime which is incompressible yet gapless. Numerical evidence for the properties of these phases is given in terms of global (compressibility, superfluid stiffness) and local (compressibility, momentum distribution) observables. 相似文献
9.
Hong T Kim YH Hotta C Takano Y Tremelling G Turnbull MM Landee CP Kang HJ Christensen NB Lefmann K Schmidt KP Uhrig GS Broholm C 《Physical review letters》2010,105(13):137207
We study the magnetic-field-induced quantum phase transition from a gapped quantum phase that has no magnetic long-range order into a gapless phase in the spin-1/2 ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY). At temperatures below about 1 K, the specific heat in the gapless phase attains an asymptotic linear temperature dependence, characteristic of a Tomonaga-Luttinger liquid. Inelastic neutron scattering and the specific heat measurements in both phases are in good agreement with theoretical calculations, demonstrating that DIMPY is the first model material for an S=1/2 two-leg spin ladder in the strong-leg regime. 相似文献
10.
We present a mean-field solution for a quantum, short-range interacting, disordered, SO(3) Heisenberg spin model, in which the Gaussian distribution of couplings is centered in an antiferromagnetic (AF) coupling J[over ]>0, and which, for weak disorder, can be treated as a perturbation of the pure AF Heisenberg system. The phase diagram contains, apart from a Néel phase at T=0, spin-glass and paramagnetic phases whose thermodynamic stability is demonstrated by an analysis of the Hessian matrix of the free-energy. The magnetic susceptibilities exhibit the typical cusp of a spin-glass transition. 相似文献
11.
We study the quantum dimer model on the triangular lattice, which is expected to describe the singlet dynamics of frustrated Heisenberg models in phases where valence bond configurations dominate their physics. We find, in contrast to the square lattice, that there is a truly short ranged resonating valence bond phase with no gapless excitations and with deconfined, gapped, spinons for a finite range of parameters. We also establish the presence of crystalline dimer phases. 相似文献
12.
对含有次近邻节点自旋交换耦合的自旋-1/2伊辛-海森伯钻石链体系进行了研究,利用矩阵对角化和传递矩阵方法对基态磁相和宏观热力学量进行了严格求解,重点探讨了所有交换耦合均为反铁磁耦合时,体系节点伊辛自旋间次近邻相互作用的影响.研究结果表明次近邻节点伊辛自旋存在反铁磁耦合时会增强系统的阻挫效应,引入破坏平移对称性的经典亚铁磁相,使基态呈现出上上上下上上的自旋构型以及磁化曲线新颖的2/3磁化平台,丰富了体系的基态相图和宏观磁性行为. 相似文献
13.
Jeong M Bert F Mendels P Duc F Trombe JC de Vries MA Harrison A 《Physical review letters》2011,107(23):237201
We report (17)O NMR measurements in the S=1/2 (Cu(2+)) kagome antiferromagnet Herbertsmithite ZnCu(3)(OH)(6)Cl(2) down to 45 mK in magnetic fields ranging from 2 to 12 T. While Herbertsmithite displays a gapless spin-liquid behavior in zero field, we uncover an instability toward a spin-solid phase at sub-Kelvin temperature induced by an applied magnetic field. The latter phase shows largely suppressed moments ?0.1 μ(B) and gapped excitations. The H-T phase diagram suggests the existence of a quantum critical point at the small but finite magnetic field μ(0)H(c)=1.55(25) T. We discuss this finding in light of the perturbative Dzyaloshinskii-Moriya interaction which was theoretically proposed to sustain a quantum critical regime for the quantum kagome Heisenberg antiferromagnet model. 相似文献
14.
The ground state, magnetization scenario and the local bipartite quantum entanglement of a mixed spin- Ising–Heisenberg model in a magnetic field on planar lattices formed by identical corner-sharing bipyramidal plaquettes is examined by combining the exact analytical concept of generalized decoration-iteration mapping transformations with Monte Carlo simulations utilizing the Metropolis algorithm. The ground-state phase diagram of the model involves six different phases, namely, the standard ferrimagnetic phase, fully saturated phase, two unique quantum ferrimagnetic phases, and two macroscopically degenerate quantum ferrimagnetic phases with two chiral degrees of freedom of the Heisenberg triangular clusters. The diversity of ground-state spin arrangement is manifested themselves in seven different magnetization scenarios with one, two or three fractional plateaus whose values are determined by the number of corner-sharing plaquettes. The low-temperature values of the concurrence demonstrate that the bipartite quantum entanglement of the Heisenberg spins in quantum ferrimagnetic phases is field independent, but twice as strong if the Heisenberg spin arrangement is unique as it is two-fold degenerate. 相似文献
15.
16.
C. Dziurzik G. I. Japaridze A. Schadschneider I. Titvinidze J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):41-51
In this paper we study the ground state phase diagram of a
one-dimensional t-J-U model away from half-filling. In the large-bandwidth
limit and for ferromagnetic exchange with easy-plane anisotropy a phase
with gapless charge and massive spin excitations, characterized by the
coexistence of triplet superconducting and spin density wave
instabilities is realized in the ground state.
With increasing ferromagnetic exchange transitions into a ferrometallic
and then a spin gapped triplet superconducting phase take place. 相似文献
17.
Batchelor M. T. Guan X.-W. Oelkers N. Ying Z.-J. 《Journal of statistical physics》2004,116(1-4):571-589
We investigate the quantum phase diagram of the exactly solved mixed spin-(1/2,1) ladder via the thermodynamic Bethe ansatz (TBA). In the absence of a magnetic field the model exhibits three quantum phases associated with su(2), su(4), and su(6) symmetries. In the presence of a strong magnetic field, there is a third and full saturation magnetization plateaux within the strong antiferromagnetic rung coupling regime. Gapless and gapped phases appear in turn as the magnetic field increases. For weak rung coupling, the fractional magnetization plateau vanishs and the model undergoes new quantum phase transitions. However, in the ferromagnetic coupling regime, the system does not have a third saturation magnetization plateau. The critical behaviour in the vicinity of the critical points is also derived systematically using the TBA. 相似文献
18.
在非绝热近似下,研究了一维spin-Peierls系统中晶格量子涨落 对系统性质的影响,讨论了系统的二聚化相变、单粒子激发和双粒子束缚态. 结果表明,量子晶格涨落会抑制晶格的二聚化,破坏系统的spin-Peierls基态稳定性.在临界点,系统发生从二聚化spin-Peierls态向无能隙态的相变. 自旋声子耦合强度对束缚态能隙的影响比单粒子激发谱能隙显著.
关键词:
sin-Peierls系统
非绝热近似
玻色化
相图 相似文献
19.
D.C. Cabra A. Honecker P. Pujol 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):55-73
We analyze the phase diagram of a system of spin-1/2 Heisenberg antiferromagnetic chains interacting through a zig-zag coupling,
also called zig-zag ladders. Using bosonization techniques we study how a spin-gap or more generally plateaux in magnetization
curves arise in different situations. While for coupled XXZchains, one has to deal with a recently discovered chiral perturbation, the coupling term which is present for normal ladders
is restored by an external magnetic field, dimerization or the presence of charge carriers. We then proceed with a numerical
investigation of the phase diagram of two coupled Heisenberg chains in the presence of a magnetic field. Unusual behaviour
is found for ferromagnetic coupled antiferromagnetic chains. Finally, for three (and more) legs one can choose different inequivalent
types of coupling between the chains. We find that the three-leg ladder can exhibit a spin-gap and/or non-trivial plateaux
in the magnetization curve whose appearance strongly depends on the choice of coupling.
Received 11 February 1999 and Received in final form 16 June 1999 相似文献
20.
Nedko B. Ivanov Svetozara I. Petrova Jürgen Schnack 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(5):121
The promotion of collinear classical spin configurations as well as the enhanced tendencytowards nearest-neighbor clustering of the quantum spins are typical features of thefrustrating isotropic three-body exchange interactions in Heisenberg spin systems. Basedon numerical density-matrix renormalization group calculations, we demonstrate that theseextra interactions in the Heisenberg chain constructed from alternating S = 3/2 and σ = 1/2 site spins can generate numerous specific quantum spinstates, including some partially-polarized ferrimagnetic states as well as adoubly-degenerate non-magnetic gapped phase. In the non-magnetic region of the phasediagram, the model describes a crossover between the spin-1 and spin-2 Haldane-typestates. 相似文献