Y. M. Vilk

Destruction of Fermi-liquid quasiparticles in two dimensions by critical fluctuations

It is shown that it is possible to quantitatively explain quantum Monte Carlo results for the Greens function of the two-dimensional Hubbard model in the weak to intermediate coupling regime. The analytic approach includes vertex corrections in a paramagnon-like self-energy. All parameters are determined self-consistently. This approach clearly shows that in two dimensions Fermi-liquid quasiparticles disappear in the paramagnetic state when the antiferromagnetic correlation length becomes larger than the electronic thermal de Broglie wavelength.

Many-body theory versus simulations for the pseudogap in the Hubbard model

The opening of a critical-fluctuation induced pseudogap (or precursor pseudogap) in the oneparticle spectral weight of the half-filled two-dimensional Hubbard model is discussed. This pseudogap, appearing in our Monte Carlo simulations, may be obtained from many-body techniques that use Green functions and vertex corrections that are at the same level of approximation. Selfconsistent theories of the Eliashberg type (such as the Fluctuation Exchange Approximation) use renormalized Green functions and bare vertices in a context where there is no Migdal theorem. They do not find the pseudogap, in quantitative and qualitative disagreement with simulations, suggesting these methods are inadequate for this problem. Differences between precursor pseudogaps and strong-coupling pseudogaps are also discussed.

ROLE OF SYMMETRY AND DIMENSION IN PSEUDOGAP PHENOMENA

The attractive Hubbard model in d=2 is studied through Monte Carlo simulations at intermediate coupling. There is a crossover temperature

Spin susceptibility of interacting electrons in one dimension: Luttinger liquid and lattice effects.

T_X

Magnetic and pair correlations of the Hubbard model with next-nearest-neighbor hopping

where a pseudogap appears with concomitant precursors of Bogoliubov quasiparticles that are not local pairs. The pseudogap in

Crossover from two- to three-dimensional critical behavior for nearly antiferromagnetic itinerant electrons

A(k,\omega)

Conserving Approximations vs. Two-Particle Self-Consistent Approach

occurs in the renormalized classical regime when the correlation length is larger than the direction-dependent thermal de Broglie wave length,

Two-particle self-consistent theory for spin and charge fluctuations in the Hubbard model

\xi_{th}=\hbar v_{F}(k)/k_{B}T.

THEORY OF MULTIPLE EXCITONIC PEAKS IN THE LUMINESCENCE SPECTRA OF DOPED QUANTUM WELLS IN A MAGNETIC FIELD

The ratio

Correlation effects on the tunneling of electrons from the surface of liquid helium.

T_{X}/T_{c}