46 research outputs found
A Dynamical Quantum Cluster Approach to Two-Particle Correlation Functions in the Hubbard Model
We investigate the charge- and spin dynamical structure factors for the 2D
one-band Hubbard model in the strong coupling regime within an extension of the
Dynamical Cluster Approximation (DCA) to two-particle response functions. The
full irreducible two-particle vertex with three momenta and frequencies is
approximated by an effective vertex dependent on the momentum and frequency of
the spin/charge excitation. In the spirit of the DCA, the effective vertex is
calculated with quantum Monte Carlo methods on a finite cluster. On the basis
of a comparison with high temperature auxiliary field quantum Monte Carlo data
we show that near and beyond optimal doping, our results provide a consistent
overall picture of the interplay between charge, spin and single-particle
excitations.Comment: 8 pages, 11 figure
The 3-Band Hubbard-Model versus the 1-Band Model for the high-Tc Cuprates: Pairing Dynamics, Superconductivity and the Ground-State Phase Diagram
One central challenge in high- superconductivity (SC) is to derive a
detailed understanding for the specific role of the - and
- orbital degrees of freedom. In most theoretical studies an
effective one-band Hubbard (1BH) or t-J model has been used. Here, the physics
is that of doping into a Mott-insulator, whereas the actual high- cuprates
are doped charge-transfer insulators. To shed light on the related question,
where the material-dependent physics enters, we compare the competing magnetic
and superconducting phases in the ground state, the single- and two-particle
excitations and, in particular, the pairing interaction and its dynamics in the
three-band Hubbard (3BH) and 1BH-models. Using a cluster embedding scheme, i.e.
the variational cluster approach (VCA), we find which frequencies are relevant
for pairing in the two models as a function of interaction strength and doping:
in the 3BH-models the interaction in the low- to optimal-doping regime is
dominated by retarded pairing due to low-energy spin fluctuations with
surprisingly little influence of inter-band (p-d charge) fluctuations. On the
other hand, in the 1BH-model, in addition a part comes from "high-energy"
excited states (Hubbard band), which may be identified with a non-retarded
contribution. We find these differences between a charge-transfer and a Mott
insulator to be renormalized away for the ground-state phase diagram of the
3BH- and 1BH-models, which are in close overall agreement, i.e. are
"universal". On the other hand, we expect the differences - and thus, the
material dependence to show up in the "non-universal" finite-T phase diagram
(-values).Comment: 17 pages, 9 figure