1,059 research outputs found
Exact many-electron ground states on the diamond Hubbard chain
Exact ground states of interacting electrons on the diamond Hubbard chain in
a magnetic field are constructed which exhibit a wide range of properties such
as flat-band ferromagnetism and correlation induced metallic, half-metallic or
insulating behavior. The properties of these ground states can be tuned by
changing the magnetic flux, local potentials, or electron density.Comment: 4 pages, 2 figure
Lattice Dimerization in the Spin-Peierls Compound CuGeO
The uniaxial pressure dependences of the exchange coupling and the structural
distortion in the dimerized phase of CuGeO are analyzed. A minimum magnetic
dimerization of 3 % is obtained, incompatible with an adiabatic approach to the
spin-Peierls transition. Exploring the properties of an Heisenberg spin chain
with dynamical spin-phonon coupling, the dimerization dependence of the spin
excitation gap is found to be in qualitative agreement with experiment.Comment: 2 pages, 1 figure include
Nature of the Peierls- to Mott-insulator transition in 1D
In order to clarify the physics of the crossover from a Peierls band
insulator to a correlated Mott-Hubbard insulator, we analyze ground-state and
spectral properties of the one-dimensional half-filled Holstein-Hubbard model
using quasi-exact numerical techniques. In the adiabatic limit the transition
is connected to the band to Mott insulator transition of the ionic Hubbard
model. Depending on the strengths of the electron-phonon coupling and the
Hubbard interaction the transition is either first order or evolves
continuously across an intermediate phase with finite spin, charge, and optical
excitation gaps.Comment: 6 pages, 7 figures to appear in EPJ
Quasiparticle anisotropy and pseudogap formation from the weak-coupling renormalization group point of view
Using the one-loop functional renormalization group technique we evaluate the
self-energy in the weak-coupling regime of the 2D t-t' Hubbard model. At van
Hove (vH) band fillings and at low temperatures the quasiparticle weight along
the Fermi surface (FS) continuously vanishes on approaching the (pi,0) point
where the quasiparticle concept is invalid. Away from vH band fillings the
quasiparticle peak is formed inside an anisotropic pseudogap and the
self-energy has the conventional Fermi-liquid characteristics near the Fermi
level. The spectral weight of the quasiparticle features is reduced on parts of
the FS between the near vicinity of hot spots and the FS points closest to
(pi,0) and (0,pi).Comment: 4 pages, 4 figures, RevTe
Exact Bond Ordered Ground State for the Transition Between the Band and the Mott Insulator
We derive an effective Hamiltonian for an ionic Hubbard chain,
valid for , where is the hopping, the Coulomb
repulsion, and the charge transfer energy. is the minimal
model for describing the transition from the band insulator (BI) () and the Mott insulator (MI) (). Using spin-particle
transformations (Phys. Rev. Lett. \textbf{86}, 1082 (2001)), we map
into an SU(3) antiferromagnetic Heisenberg model whose
exact ground state is known. In this way, we show rigorously that a
spontaneously dimerized insulating ferroelectric phase appears in the
transition region between the BI and MI
From local to nonlocal Fermi liquid in doped antiferromagnets
The variation of single-particle spectral functions with doping is studied
numerically within the t-J model. It is shown that corresponding self energies
change from local ones at the intermediate doping to strongly nonlocal ones for
a weakly doped antiferromagnet. The nonlocality shows up most clearly in the
pseudogap emerging in the density of states, due to the onset of short-range
antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let
On different lagrangian formalisms for vector resonances within chiral perturbation theory
We study the relation of vector Proca field formalism and antisymmetric
tensor field formalism for spin-one resonances in the context of the large N_C
inspired chiral resonance Lagrangian systematically up to the order O(p6) and
give a transparent prescription for the transition from vector to antisymmetric
tensor Lagrangian and vice versa. We also discuss the possibility to describe
the spin-one resonances using an alternative "mixed" first order formalism,
which includes both types of fields simultaneously, and compare this one with
the former two. We also briefly comment on the compatibility of the above
lagrangian formalisms with the high-energy constraints for concrete VVP
correlator.Comment: 34 pages, 3 figure
Remnant Fermi Surfaces in Photoemission
Recent experiments have introduced a new concept for analyzing the
photoemission spectra of correlated electrons -- the remnant Fermi surface
(rFs), which can be measured even in systems which lack a conventional Fermi
surface. Here, we analyze the rFs in a number of interacting electron models,
and find that the results fall into two classes. For systems with pairing
instabilities, the rFs is an accurate replica of the true Fermi surface. In the
presence of nesting instabilities, the rFs is a map of the resulting
superlattice Brillouin zone. The results suggest that the gap in Ca_2CuO_2Cl_2
is of nesting origin.Comment: 4 pages LaTex, 3 ps figure
Suppression of static stripe formation by next-neighbor hopping
We show from real-space Hartree-Fock calculations within the extended Hubbard
model that next-nearest neighbor (t') hopping processes act to suppress the
formation of static charge stripes. This result is confirmed by investigating
the evolution of charge-inhomogeneous corral and stripe phases with increasing
t' of both signs. We propose that large t' values in YBCO prevent static stripe
formation, while anomalously small t' in LSCO provides an additional reason for
the appearance of static stripes only in these systems.Comment: 4 pages, 5 figure
Disorder Induced Stripes in d-Wave Superconductors
Stripe phases are observed experimentally in several copper-based high-Tc
superconductors near 1/8 hole doping. However, the specific characteristics may
vary depending on the degree of dopant disorder and the presence or absence of
a low- temperature tetragonal phase. On the basis of a Hartree-Fock decoupling
scheme for the t-J model we discuss the diverse behavior of stripe phases. In
particular the effect of inhomogeneities is investigated in two distinctly
different parameter regimes which are characterized by the strength of the
interaction. We observe that small concen- trations of impurities or vortices
pin the unidirectional density waves, and dopant disorder is capable to
stabilize a stripe phase in parameter regimes where homogeneous phases are
typically favored in clean systems. The momentum-space results exhibit
universal features for all coexisting density-wave solutions, nearly unchanged
even in strongly disordered systems. These coexisting solutions feature
generically a full energy gap and a particle-hole asymmetry in the density of
states.Comment: 28 pages, 8 figure
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