G. Uhrig | Searcharxiv

arXiv1995

Ferromagnetism in the Hubbard model on the square lattice: Improved instability criterion for the Nagaoka state

The instability of the fully polarized ferromagnetic state (Nagaoka state) with respect to single spin flips is re-examined for the Hubbard model on the square lattice with a large family of variational wave functions which include correlation effects of the majority spins in the vicinity of the flipped spin. We find a critical hole density of $δ_{cr} = 0.251$ for $U = \infty$ and a critical coupling of $U_{cr} = 77.7 t$. Both values improve previous variational results considerably.

cond-mat↗

arXiv1995

Drude weight and dc-conductivity of correlated electrons

The Drude weight $D$ and the dc-conductivity $σ_{dc} (T)$ of strongly correlated electrons are investigated theoretically. Analytic results are derived for the homogeneous phase of the Hubbard model in $d = \infty$ dimensions, and for spinless fermions in this limit with $1/d$-corrections systematically included to lowest order. It is found that $σ_{dc}(T)$ is finite for all $T > 0$, displaying Fermi liquid behavior, $σ_{dc} \propto 1/T^2$, at low temperatures. The validity of this result for finite dimensions is examined by investigating the importance of Umklapp scattering processes and vertex corrections. A finite dc-conductivity for $T > 0$ is argued to be a generic feature of correlated lattice electrons in not too low dimensions.

cond-mat↗