8,078 research outputs found
Ground state of an distorted diamond chain - model of
We study the ground state of the model Hamiltonian of the trimerized
quantum Heisenberg chain in which
the non-magnetic ground state is observed recently. This model consists of
stacked trimers and has three kinds of coupling constants between spins; the
intra-trimer coupling constant and the inter-trimer coupling constants
and . All of these constants are assumed to be antiferromagnetic. By
use of the analytical method and physical considerations, we show that there
are three phases on the plane (, ), 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 the excitation gap between the
two-fold degenerate ground state and the first excited state, which explains
the non-magnetic ground state observed in . We also obtain the phase diagram on the
plane from the numerical diagonalization data for finite systems by use of the
Lanczos algorithm.Comment: LaTeX2e, 15 pages, 21 eps figures, typos corrected, slightly detailed
explanation adde
Magnetization Plateau of an S=1 Frustrated Spin Ladder
We study the magnetization plateau at 1/4 of the saturation magnetization of
the S=1 antiferromagnetic spin ladder both analytically and numerically, with
the aim of explaining recent experimental results on BIP-TENO by Goto et al. We
propose two mechanisms for the plateau formation and clarify the plateau phase
diagram on the plane of the coupling constants between spins
Ground-State Phase Diagram of the XXZ Model on a Railroad-Trestle Lattice with Asymmetric Leg Interactions
Using the bosonization and level spectroscopy methods, we study the
ground-state phase diagram of a XXZ antiferromagnet on a railroad-trestle
lattice with asymmetric leg interactions. It is shown that the asymmetry does
not change the dimer/Neel transition line significantly, which agrees with the
expectation based on a naive bosonization procedure, but it does change the
dimer/spin-fluid transition line. To understand this observation, we analyze
eigenvectors of the ground state, dimer excitation, doublet excitation and Neel
excitation, and find that only the doublet excitation is affected by the
asymmetric interaction.Comment: 6 pages, 11 Postscript figures, use jpsj2.cl
Numerical and approximate analytical results for the frustrated spin-1/2 quantum spin chain
We study the frustrated phase of the quantum spin-
system with nearest-neighbour and next-nearest-neighbour isotropic exchange
known as the Majumdar-Ghosh Hamiltonian. We first apply the coupled-cluster
method of quantum many-body theory based on a spiral model state to obtain the
ground state energy and the pitch angle. These results are compared with
accurate numerical results using the density matrix renormalisation group
method, which also gives the correlation functions. We also investigate the
periodicity of the phase using the Marshall sign criterion. We discuss
particularly the behaviour close to the phase transitions at each end of the
frustrated phase.Comment: 17 pages, Standard Latex File + 7 PostScript figures in separate
file. Figures also can also be requested from [email protected]
Breakdown of the Luttinger sum-rule at the Mott-Hubbard transition in the one-dimensional t1-t2 Hubbard model
We investigate the momentum distribution function near the Mott-Hubbard
transition in the one-dimensional t1-t2 Hubbard model (the zig-zag Hubbard
chain), with the density-matrix renormalization-group technique. We show that
for strong interactions the Mott-Hubbard transition occurs between the
metallic-phase and an insulating dimerized phase with incommensurate spin
excitations, suggesting a decoupling of magnetic and charge excitations not
present in weak coupling. We illustrate the signatures for the Mott-Hubbard
transition and the commensurate-incommensurate transition in the insulating
spin-gapped state in their respective ground-state momentum distribution
functions
Mechanisms for Non-Trivial Magnetization Plateaux of an S=1 Frustrated Spin Ladder
We investigate the non-trivial magnetization plateau at 1/4 of the saturation
magnetization of S=1 spin ladder, especially with reference to recent
experimental results on a new organic tetraradical
3,3',5,5'-tetrakis(N-tert-butylaminoxyl)biphenyl, abbreviated as BIP-TENO. We
propose three mechanisms for the formation of the plateau; the Neel mechanism,
the dimer mechanism and the spin-Peierls mechanism. We also discuss the effect
of four-spin exchange interactions.Comment: 3 pages, 5 figures, Orbital2001 (International Conference on Strongly
Correlated Electrons with Orbital Degrees of Freedom) (September 11-14, 2001.
Sendai
Possibility of f-wave spin-triplet superconductivity in the CoO superconductor: a case study on a 2D triangular lattice in the repulsive Hubbard model
Stimulated by the recent finding of NaCoO.1.3HO
superconductor, we investigate superconducting instabilities on a 2D triangular
lattice in the repulsive Hubbard model. Using the third-order perturbation
expansion with respect to the on-site repulsion , we evaluate the linearized
Dyson-Gor'kov equation. We find that an -wave spin-triplet pairing is the
most stable in a wide range of the next nearest neighbor hopping integral
and an electron number density . The introduction of is crucial to
adjust the van Hove singularities to the neighborhood of the Fermi surface
crossing around K point. In this case, the bare spin susceptibility shows the
broad peak around point. These conditions stabilize the -wave
pairing. Although the -wave pairing is also given by the
fluctuation-exchange approximation, the transition temperature is too low to be
observed. This is because the depairing effect by the spin fluctuation is
over-estimated. Thus, the third-order vertex corrections are important for the
spin-triplet superconductivity, like the case in SrRuO.Comment: 4 pages, 7 figure
Onset of incommensurability in quantum spin chains
In quantum spin chains, it has been observed that the incommensurability
occurs near valence-bond-solid (VBS)-type solvable points, and the correlation
length becomes shortest at VBS-type points. Besides, the correlation function
decays purely exponentially at VBS-type points, in contrast with the
two-dimensional (2D) Ornstein-Zernicke type behavior in the other region with
an excitation gap. We propose a mechanism to explain the onset of the
incommensurability and the shortest correlation length at VBS-like points. This
theory can be applicable for more general cases.Comment: 9 pages, 2 figure
Higgsless Theory of Electroweak Symmetry Breaking from Warped Space
We study a theory of electroweak symmetry breaking without a Higgs boson,
recently suggested by Csaki et al. The theory is formulated in 5D warped space
with the gauge bosons and matter fields propagating in the bulk. In the 4D dual
picture, the theory appears as the standard model without a Higgs field, but
with an extra gauge group G which becomes strong at the TeV scale. The strong
dynamics of G breaks the electroweak symmetry, giving the masses for the W and
Z bosons and the quarks and leptons. We study corrections in 5D which are
logarithmically enhanced by the large mass ratio between the Planck and weak
scales, and show that they do not destroy the structure of the electroweak
gauge sector at the leading order. We introduce a new parameter, the ratio
between the two bulk gauge couplings, into the theory and find that it allows
us to control the scale of new physics. We also present a potentially realistic
theory accommodating quarks and leptons and discuss its implications, including
the violation of universality in the W and Z boson couplings to matter and the
spectrum of the Kaluza-Klein excitations of the gauge bosons. The theory
reproduces many successful features of the standard model, although some
cancellations may still be needed to satisfy constraints from the precision
electroweak data.Comment: 17 pages, Latex; important correction in discussions on effects from
brane terms, reference adde
Dynamic Transition in the Structure of an Energetic Crystal during Chemical Reactions at Shock Front Prior to Detonation
Mechanical stimuli in energetic materials initiate chemical reactions at shock fronts prior to detonation. Shock sensitivity measurements provide widely varying results, and quantum-mechanical calculations are unable to handle systems large enough to describe shock structure. Recent developments in reactive force-field molecular dynamics (ReaxFF-MD) combined with advances in parallel computing have paved the way to accurately simulate reaction pathways along with the structure of shock fronts. Our multimillion-atom ReaxFF-MD simulations of l,3,5-trinitro-l,3,5-triazine (RDX) reveal that detonation is preceded by a transition from a diffuse shock front with well-ordered molecular dipoles behind it to a disordered dipole distribution behind a sharp front
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