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Quantum Monte Carlo and exact diagonalization study of a dynamic Hubbard model

cond-mat/0201005 (Los Alamos)
,
Phys.Rev. B65, 214510 (2002)
.
A one-dimensional model of electrons locally coupled to spin-1/2 degrees of freedom
is studied by numerical techniques. The model is one in the class of $dynamic$
$Hubbard$ $models$ that describe the relaxation of an atomic orbital upon double
electron occupancy due to electron-electron interactions. We study the parameter
regime where pairing occurs in this model by exact diagonalization of small
clusters. World line quantum Monte Carlo simulations support the results of exact
diagonalization for larger systems and show that kinetic energy is lowered
when pairing occurs. The qualitative physics of this model and
others in its class, obtained through approximate analytic calculations, is that
superconductivity occurs through hole undressing even in parameter
regimes where the effective on-site interaction is strongly repulsive.
Our numerical results confirm the expected qualitative behavior, and
show that pairing will occur in a substantially larger parameter
regime than predicted by the approximate low energy effective Hamiltonian.

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