155 research outputs found
Spectral properties of the 2D Holstein polaron
The two-dimensional Holstein model is studied by means of direct Lanczos
diagonalization preserving the full dynamics and quantum nature of phonons. We
present numerical exact results for the single-particle spectral function, the
polaronic quasiparticle weight, and the optical conductivity. The polaron band
dispersion is derived both from exact diagonalization of small lattices and
analytic calculation of the polaron self-energy.Comment: 8 pages, revtex, 6 figure
Spectral properties of the 2D Holstein t-J model
Employing the Lanczos algorithm in combination with a kernel polynomial
moment expansion (KPM) and the maximum entropy method (MEM), we show a way of
calculating charge and spin excitations in the Holstein t-J model, including
the full quantum nature of phonons. To analyze polaron band formation we
evaluate the hole spectral function for a wide range of electron-phonon
coupling strengths. For the first time, we present results for the optical
conductivity of the 2D Holstein t-J model.Comment: 2 pages, Latex. Submitted to Physica C, Proc. Int. Conf. on M2HTSC
Parallelization Strategies for Density Matrix Renormalization Group Algorithms on Shared-Memory Systems
Shared-memory parallelization (SMP) strategies for density matrix
renormalization group (DMRG) algorithms enable the treatment of complex systems
in solid state physics. We present two different approaches by which
parallelization of the standard DMRG algorithm can be accomplished in an
efficient way. The methods are illustrated with DMRG calculations of the
two-dimensional Hubbard model and the one-dimensional Holstein-Hubbard model on
contemporary SMP architectures. The parallelized code shows good scalability up
to at least eight processors and allows us to solve problems which exceed the
capability of sequential DMRG calculations.Comment: 18 pages, 9 figure
On the stability of polaronic superlattices in strongly coupled electron-phonon systems
We investigate the interplay of electron-phonon (EP) coupling and strong
electronic correlations in the frame of the two-dimensional (2D) Holstein t-J
model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled
band case. The use of direct Lanczos diagonalization on finite lattices allows
us to include the effects of quantum phonon fluctuations in the calculation of
spin/charge structure factors and hole-phonon correlation functions. In the
adiabatic strong coupling regime we found evidence for ``self-localization'' of
polaronic carriers in a charge-modulated structure, a type of
superlattice solidification reminiscent of those observed in the nickel
perovskites .Comment: 2 pages, Latex. Submitted to Physica C, Proc. Int. Conf. on M2HTSC
Polaronic effects in strongly coupled electron-phonon systems: Exact diagonalization results for the 2D Holstein t-J model
Ground-state and dynamical properties of the 2D Holstein t-J model are
examined by means of direct Lanczos diagonalization, using a truncation method
of the phononic Hilbert space. The single-hole spectral function shows the
formation of a narrow hole-polaron band as the electron-phonon coupling
increases, where the polaronic band collapse is favoured by strong Coulomb
correlations. In the two-hole sector, the hole-hole correlations unambiguously
indicate the existence of inter-site bipolaronic states. At quarter-filling, a
polaronic superlattice is formed in the adiabatic strong-coupling regime.Comment: 3 pages, LaTeX, 6 Postscript figures, Proc. Int. Conf. on Strongly
Correlated Electron Systems, Zuerich, August 1996, accepted for publication
in Physica
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
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