Nonlocal dynamical correlations in the Hubbard model: A noncrossing approximation study.

Tran Minh-Tien

We study the two-dimensional Hubbard model by means of an extension of the dynamical mean-field approximation (DMFA). The extension is based on the projection technique and the DMFA, in which nonlocal contributions to the dynamics of the system are taken into account through static short-ranged correlations, while dynamical local contributions are kept by the local self-energy. The short-ranged correlations and the local self-energy are determined by mapping the lattice problem onto a self-consistently embedded cluster. We solve the cluster problem by using a noncrossing approximation. The spectral function obtained satisfies the sum rules of its first four moments. The spectra display pronounced nonlocal features including a pseudogap near the Fermi surface due to a competition between the Kondo-singlet formation and short-range spin correlations.

E. G. Goryachev, Evgeniy V. Kuz’min

Hanna Terletska, Tianran Chen, Emanuel Gull

Martin Eckstein, Philipp Werner

We solve the impurity problem which arises within nonequilibrium dynamical mean-field theory for the Hubbard model by means of a self-consistent perturbation expansion around the atomic limit. While the lowest order, known as the noncrossing approximation (NCA), is reliable only when the interaction $U$ is much larger than the bandwidth, low-order corrections to the NCA turn out to be sufficient to reproduce numerically exact Monte Carlo results in a wide parameter range that covers the insulating phase and the metal-insulator crossover regime at not too low temperatures. As an application of the perturbative strong-coupling impurity solver we investigate the response of the double occupancy in the Mott insulating phase of the Hubbard model to a dynamical change in the interaction or the hopping, a technique which has been used as a probe of the Mott insulating state in ultracold fermionic gases.

P. Lombardo, R. Hayn, G. I. Japaridze

We investigate the metal-insulator transitions at finite temperature for the Hubbard model with diagonal alloy disorder. We solve the dynamical mean-field-theory equations with the noncrossing approximation and we use the coherent potential approximation to handle disorder. The excitation spectrum is given for various correlation strength $U$ and disorder. Two successive metal-insulator transitions are observed at integer-filling values as $U$ is increased. An important selective transfer of spectral weight arises upon doping. The strong influence of the temperature on the low-energy dynamics is studied in detail.

J. M. P. Carmelo, D. Baeriswyl, X. Zotos