Charge inhomogeneity coexisting with large Fermi surfaces

We discuss how stripes in cuprates can be compatible with a Fermi-liquid-like Fermi surface and, at the same time, they give rise to a one-dimensional-like pseudo Fermi surface in the momentum distribution function.Comment: Proceedings of the M2S conference, July 2006, Dresden; 2 pages, 1 figure to appear on Phisica

Fermi surface dichotomy on systems with fluctuating order

We investigate the effect of a dynamical collective mode coupled with quasiparticles at specific wavevectors only. This coupling describes the incipient tendency to order and produces shadow spectral features at high energies, while leaving essentially untouched the low energy quasiparticles. This allows to interpret seemingly contradictory experiments on underdoped cuprates, where many converging evidences indicate the presence of charge (stripe or checkerboard) order, which remains instead elusive in the Fermi surface obtained from angle-resolved photoemission experiments.Comment: 11 pages, 10 figure

Phonon renormalization from local and transitive electron-lattice couplings in strongly correlated systems

Within the time-dependent Gutzwiller approximation (TDGA) applied to Holstein- and SSH-Hubbard models we study the influence of electron correlations on the phonon self-energy. For the local Holstein coupling we find that the phonon frequency renormalization gets weakened upon increasing the onsite interaction $U$ for all momenta. In contrast, correlations can enhance the phonon frequency shift for small wave-vectors in the SSH-Hubbard model. Moreover the TDGA applied to the latter model provides a mechanism which leads to phonon frequency corrections at intermediate momenta due to the coupling with double occupancy fluctuations. Both models display a shift of the nesting-induced to a $q=0$ instability when the onsite interaction becomes sufficiently strong and thus establishing phase separation as a generic phenomenon of strongly correlated electron-phonon coupled systems.Comment: 14 pages, 11 figure

Exotic quantum spin models in spin-orbit-coupled Mott insulators

We study cold atoms in an optical lattice with synthetic spin-orbit coupling in the Mott-insulator regime. We calculate the parameters of the corresponding tight-binding model using Peierls substitution and "localized Wannier states method" and derive the low-energy spin Hamiltonian for fermions and bosons. The spin Hamiltonian is a combination of Heisenberg model, quantum compass model and Dzyaloshinskii-Moriya interactions and it has a rich classical phase diagram with collinear, spiral and vortex phases.Comment: 5 pages, 3 color figure

Charge instabilities and electron-phonon interaction in the Hubbard-Holstein model

We consider the Hubbard-Holstein model in the adiabatic limit to investigate the effects of electron-electron interactions on the electron-phonon coupling. To this aim we compute at any momentum and filling the static charge susceptibility of the Hubbard model within the Gutzwiller approximation and we find that electron-electron correlations effectively screen the electron coupling to the lattice. This screening is more effective at large momenta and, as a consequence, the charge-density wave phase due to the usual Peierls instability of the Fermi surface momenta is replaced by a phase-separation instability when the correlations are sizable.Comment: 15 pages, 12 figure

The composite operator method route to the 2D Hubbard model and the cuprates

In this review paper, we illustrate a possible route to obtain a reliable solution of the 2D Hubbard model and an explanation for some of the unconventional behaviours of underdoped high-T_c cuprate superconductors within the framework of the composite operator method. The latter is described exhaustively in its fundamental philosophy, various ingredients and robust machinery to clarify the reasons behind its successful applications to many diverse strongly correlated systems, controversial phenomenologies and puzzling materials