300 research outputs found
Low-Temperature Dynamical Structure Factor of the Two-Leg Spin-1/2 Heisenberg Ladder
We determine the dynamical structure factor of the two-leg spin-1/2
Heisenberg ladder at low temperatures in the regime of strong rung coupling.
The dominant feature at zero temperature is the coherent triplon mode. We show
that the lineshape of this mode broadens in a non-symmetric way at finite
temperatures and that the degree of asymmetry increases with temperature. We
also show that at low frequencies a temperature induced resonance akin to the
Villain mode in the spin-1/2 Heisenberg Ising chain emerges.Comment: 13 pages, 7 figures, revte
Local density of states of 1D Mott insulators and CDW states with a boundary
We determine the local density of states (LDOS) of one-dimensional
incommensurate charge density wave (CDW) states in the presence of a strong
impurity potential, which is modeled by a boundary. We find that the CDW gets
pinned at the impurity, which results in a singularity in the Fourier transform
of the LDOS at momentum 2k_F. At energies above the spin gap we observe
dispersing features associated with the spin and charge degrees of freedom
respectively. In the presence of an impurity magnetic field we observe the
formation of a bound state localized at the impurity. All of our results carry
over to the case of one dimensional Mott insulators by exchanging the roles of
spin and charge degrees of freedom. We discuss the implications of our result
for scanning tunneling microscopy experiments on spin-gap systems such as
two-leg ladder cuprates and 1D Mott insulators
Dynamical response functions in the quantum Ising chain with a boundary
We determine dynamical response functions in the scaling limit of the quantum Ising chain on the half line in
the presence of a boundary magnetic field. Using a spectral representation in
terms of infinite volume form factors and a boundary state, we derive an
expansion for the correlator that is found to be rapidly convergent as long as
|\frac{x_1+x_2}{\xi}|\agt 0.2 where is the correlation length. At
sufficiently late times we observe oscillatory behaviour of the correlations
arbitrarily far away from the boundary. We investigate the effects of the
boundary bound state that is present for a range of boundary magnetic fields.Comment: 32 page
Boundary effects on the local density of states of one-dimensional Mott insulators and charge density wave states
We determine the local density of states (LDOS) for spin-gapped
one-dimensional charge density wave (CDW) states and Mott insulators in the
presence of a hard-wall boundary. We calculate the boundary contribution to the
single-particle Green function in the low-energy limit using field theory
techniques and analyze it in terms of its Fourier transform in both time and
space. The boundary LDOS in the CDW case exhibits a singularity at momentum
2kF, which is indicative of the pinning of the CDW order at the impurity. We
further observe several dispersing features at frequencies above the spin gap,
which provide a characteristic signature of spin-charge separation. This
demonstrates that the boundary LDOS can be used to infer properties of the
underlying bulk system. In presence of a boundary magnetic field mid-gap states
localized at the boundary emerge. We investigate the signature of such bound
states in the LDOS. We discuss implications of our results on STM experiments
on quasi-1D systems such as two-leg ladder materials like Sr14Cu24O41. By
exchanging the roles of charge and spin sectors, all our results directly carry
over to the case of one-dimensional Mott insulators.Comment: 28 page
Dynamical density correlation function of 1D Mott insulators in a magnetic field
We consider the one dimensional (1D) extended Hubbard model at half filling
in the presence of a magnetic field. Using field theory techniques we calculate
the dynamical density-density correlation function in the
low-energy limit. When excitons are formed, a singularity appears in
at a particular energy and momentum transfer.Comment: 7 pages, 4 figure
Eight state supersymmetric model of strongly correlated fermions
An integrable eight state supersymmtric model is proposed, which is a
fermion model with correlated single-particle and pair hoppings as well as
uncorrelated triple-particle hopping. It has an supersymmetry and
contains one symmetry-preserving free parameter. The model is solved and the
Bethe ansatz equations are obtained.Comment: Some cosmetic changes; to appear in Phys. Rev.
Ising Deconfinement Transition Between Feshbach-Resonant Superfluids
We investigate the phase diagram of bosons interacting via Feshbach-resonant
pairing interactions in a one-dimensional lattice. Using large scale density
matrix renormalization group (DMRG) and field theory techniques we explore the
atomic and molecular correlations in this low-dimensional setting. We provide
compelling evidence for an Ising deconfinement transition occurring between
distinct superfluids and extract the Ising order parameter and correlation
length of this unusual superfluid transition. This is supported by results for
the entanglement entropy which reveal both the location of the transition and
critical Ising degrees of freedom on the phase boundary.Comment: 4 pages, 4 figure
The one-dimensional Hubbard model with open ends: Universal divergent contributions to the magnetic susceptibility
The magnetic susceptibility of the one-dimensional Hubbard model with open
boundary conditions at arbitrary filling is obtained from field theory at low
temperatures and small magnetic fields, including leading and next-leading
orders. Logarithmic contributions to the bulk part are identified as well as
algebraic-logarithmic divergences in the boundary contribution. As a
manifestation of spin-charge separation, the result for the boundary part at
low energies turns out to be independent of filling and interaction strength
and identical to the result for the Heisenberg model. For the bulk part at zero
temperature, the scale in the logarithms is determined exactly from the Bethe
ansatz. At finite temperature, the susceptibility profile as well as the
Friedel oscillations in the magnetisation are obtained numerically from the
density-matrix renormalisation group applied to transfer matrices. Agreement is
found with an exact asymptotic expansion of the relevant correlation function.Comment: 30 pages, 8 figures, reference adde
Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4
We study dynamical properties of the anisotropic triangular quantum
antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have
established that the dynamical spin correlations cannot be understood within a
linear spin wave analysis. We go beyond linear spin wave theory by taking
interactions between magnons into account in a 1/S expansion. We determine the
dynamical structure factor and carry out extensive comparisons with
experimental data. We find that compared to linear spin wave theory a
significant fraction of the scattering intensity is shifted to higher energies
and strong scattering continua are present. However, the 1/S expansion fails to
account for the experimentally observed large quantum renormalization of the
exchange energies.Comment: 13 pages, 11 figures, higher quality figures can be obtained from the
author
Exact solution and finite size properties of the vertex model
We have diagonalized the transfer matrix of the vertex
model by means of the algebraic Bethe ansatz method for a variety of grading
possibilities. This allowed us to investigate the thermodynamic limit as well
as the finite size properties of the corresponding spin chain in the massless
regime. The leading behaviour of the finite size corrections to the spectrum is
conjectured for arbitrary . For we find a critical line with central
charge whose exponents vary continuously with the -deformation
parameter. For the finite size term related to the conformal anomaly
depends on the anisotropy which indicates a multicritical behaviour typical of
loop models.Comment: 40 pages, 8 figures, late
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