763 research outputs found
Relationship between single-particle excitation and spin excitation at the Mott Transition
An intuitive interpretation of the relationship between the dispersion
relation of the single-particle excitation in a metal and that of the spin
excitation in a Mott insulator is presented, based on the results for the one-
and two-dimensional Hubbard models obtained by using the Bethe ansatz,
dynamical density-matrix renormalization group method, and cluster perturbation
theory. The dispersion relation of the spin excitation in the Mott insulator is
naturally constructed from that of the single-particle excitation in the
zero-doping limit in both one- and two-dimensional Hubbard models, which allows
us to interpret the doping-induced states as the states that lose charge
character toward the Mott transition. The characteristic feature of the Mott
transition is contrasted with the feature of a Fermi liquid and that of the
transition between a band insulator and a metal.Comment: 6 pages, 2 figures, to appear in JPS Conf. Pro
Dynamical Magnetic Susceptibilities in Cu Benzoate
Recent experiments on the quasi 1-D antiferromagnet Cu Benzoate revealed a
magentic field induced gap coexisting with (ferro)magnetic order. A theory
explaining these findings has been proposed by Oshikawa and Affleck. In the
present work we discuss consequences of this theory for inelastic neutron
scattering experiments by calculating the dynamical magnetic susceptibilities
close to the antiferromagnetic wave vector by the formfactor method.Comment: 6 pages of revtex, 9 figures, extended comparison with experimen
Applications of Massive Integrable Quantum Field Theories to Problems in Condensed Matter Physics
We review applications of the sine-Gordon model, the O(3) non-linear sigma
model, the U(1) Thirring model, and the O(N) Gross--Neveu model to quasi
one-dimensional quantum magnets, Mott insulators, and carbon nanotubes. We
focus upon the determination of dynamical response functions for these
problems. These quantities are computed by means of form factor expansions of
quantum correlation functions in integrable quantum field theories. This
approach is reviewed here in some detail.Comment: 150 pages, 35 figures, published in the I. Kogan Memorial Volume by
World Scientifi
Effects of thermal phase fluctuations in a 2D superconductor: an exact result for the spectral function
We consider the single particle spectral function for a two-dimensional clean
superconductor in a regime of strong critical thermal phase fluctuations. In
the limit where the maximum of the superconducting gap is much smaller than the
Fermi energy we obtain an exact expression for the spectral function integrated
over the momentum component perpendicular to the Fermi surface.Comment: 4 pages, 3 figures. References added, figures improve
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
A Numerical Renormalization Group for Continuum One-Dimensional Systems
We present a renormalization group (RG) procedure which works naturally on a
wide class of interacting one-dimension models based on perturbed (possibly
strongly) continuum conformal and integrable models. This procedure integrates
Kenneth Wilson's numerical renormalization group with Al. B. Zamolodchikov's
truncated conformal spectrum approach. Key to the method is that such theories
provide a set of completely understood eigenstates for which matrix elements
can be exactly computed. In this procedure the RG flow of physical observables
can be studied both numerically and analytically. To demonstrate the approach,
we study the spectrum of a pair of coupled quantum Ising chains and correlation
functions in a single quantum Ising chain in the presence of a magnetic field.Comment: 4 pages, 4 figure
"Light-cone" dynamics after quantum quenches in spin chains
Signal propagation in the non equilibirum evolution after quantum quenches
has recently attracted much experimental and theoretical interest. A key
question arising in this context is what principles, and which of the
properties of the quench, determine the characteristic propagation velocity.
Here we investigate such issues for a class of quench protocols in one of the
central paradigms of interacting many-particle quantum systems, the spin-1/2
Heisenberg XXZ chain. We consider quenches from a variety of initial thermal
density matrices to the same final Hamiltonian using matrix product state
methods. The spreading velocities are observed to vary substantially with the
initial density matrix. However, we achieve a striking data collapse when the
spreading velocity is considered to be a function of the excess energy. Using
the fact that the XXZ chain is integrable, we present an explanation of the
observed velocities in terms of "excitations" in an appropriately defined
generalized Gibbs ensemble.Comment: 4+pages, 5 figures, supplementary materia
Superconductivity generated by coupling to a Cooperon in a 2-dimensional array of 4-leg Hubbard ladders
Starting from an array of four-leg Hubbard ladders weakly doped away from
half-filling and weakly coupled by inter-ladder tunneling, we derive an
effective low energy model which contains a partially truncated Fermi surface
and a well defined Cooperon excitation formed by a bound pair of holes. An
attractive interaction in the Cooper channel is generated on the Fermi surface
through virtual scattering into the Cooperon state. Although the model is
derived in the weak coupling limit of a four-leg ladder array, an examination
of exact results on finite clusters for the strong coupling t-J model suggests
the essential features are also present for a strong coupling Hubbard model on
a square lattice near half-filling.Comment: 20 pages, 4 figure
On the origin of the Fermi arc phenomena in the underdoped cuprates: signature of KT-type superconducting transition
We study the effect of thermal phase fluctuation on the electron spectral
function in a d-wave superconductor with Monte Carlo simulation.
The phase degree of freedom is modeled by a XY-type model with build-in d-wave
character. We find a ridge-like structure emerges abruptly on the underlying
Fermi surface in above the KT-transition temperature of the XY
model. Such a ridge-like structure, which shares the same characters with the
Fermi arc observed in the pseudogap phase of the underdoped cuprates, is found
to be caused by the vortex-like phase fluctuation of the XY model.Comment: 5 page
Spectral Properties near the Mott Transition in the One-Dimensional Hubbard Model
Single-particle spectral properties near the Mott transition in the
one-dimensional Hubbard model are investigated by using the dynamical
density-matrix renormalization group method and the Bethe ansatz. The
pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard
band are explained in terms of spinons, holons, antiholons, and doublons. The
Mott transition is characterized by the emergence of a gapless mode whose
dispersion relation extends up to the order of hopping t (spin exchange J) in
the weak (strong) interaction regime caused by infinitesimal doping.Comment: 4 pages, 2 figure
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