21 research outputs found
Frequency-dependent spin susceptibility in the two-dimensional Hubbard model
A Quantum Monte Carlo calculation of dynamical spin susceptibility in the
half-filled 2D Hubbard model is presented for temperature and an
intermediate on-site repulsion . Using the singular value decomposition
technique we succeed in analytically continuing the Matsubara Green's function
into the real frequency domain and in deriving the spectral representation for
the longitudinal and transverse spin susceptibility. The simulation results,
while contradicting the random-phase approximation prediction of
antiferromagnetic long-range order at this temperature, are in agreement with
an extension of a self-consistent renormalization approach of Moriya. The
static susceptibility calculated using this technique is qualitatively
consistent with the simulation results.Comment: 4 pages, Revtex, encoded figs.uu file with 3 figures enclose
Spectral weight function for the half-filled Hubbard model: a singular value decomposition approach
The singular value decomposition technique is used to reconstruct the
electronic spectral weight function for a half-filled Hubbard model with
on-site repulsion from Quantum Monte Carlo data. A two-band structure
for the single-particle excitation spectrum is found to persist as the lattice
size exceeds the spin-spin correlation length. The observed bands are flat in
the vicinity of the points in the Brillouin zone, in
accordance with experimental data for high-temperature superconducting
compounds.Comment: 4 pages, Revtex
Results on Finite Density QCD
A brief summary of the formulation of QCD at finite chemical potental, ,
is presented. The failure of the quenched approximation to the problem is
reviewed.
Results are presented for dynamical simulations of the theory at strong and
intermediate couplings. We find that the problems associated with the quenched
theory persist: the onset of non-zero quark number does seem to occur at a
chemical potential . However analysis of the
Lee-Yang zeros of the grand canonical partition function in the complex
fugacity plane, (), does show signals of critical behaviour in the
expected region of chemical potential.
Results are presented for a simulation at finite density of the Gross-Neveu
model on a lattice near to the chiral limit. Contrary to our simulations
of QCD no pathologies were found when passed through the value
m_{\pi}/2}.Comment: 14 pages, Latex, 18 eps figures, Review for Tsukuba worksho
Density-Induced Breaking of Pairs in the Attractive Hubbard Model
A conserving T-matrix approximation is applied to the two-dimensional
attractive Hubbard model in the low-density regime. A set of self-consistent
equations is solved in the real-frequency domain to avoid the analytic
continuation procedure. By tuning the chemical potential the particle density
was varied in the limits 0.01 < n < 0.18. For the value of the attractive
potential U=8t the binding energy of pairs monotonically decreases with
increasing n, from its zero-density limit 2.3t and vanishes at a critical
density n=0.19. A pairing-induced pseudogap in the single-particle density of
states is found at low densities and temperatures.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
Singularity of the density of states in the two-dimensional Hubbard model from finite-size scaling of Yang-Lee zeros
A finite size scaling is applied to the Yang-Lee zeros of the grand canonical
partition function for the 2-D Hubbard model in the complex chemical potential
plane. The logarithmic scaling of the imaginary part of the zeros with the
system size indicates a singular dependence of the carrier density on the
chemical potential. Our analysis points to a second-order phase transition with
critical exponent which leads to a
divergence of the electronic susceptibility. We interprete these results as
reflecting singular behaviour of the density of states in the quasiparticle
spectrum.Comment: 8 pages, Revte