J. Costa-Quintana

Mott transition in the two-dimensional Hubbard model

Abstract We are interested in the description of the Mott–Hubbard transition from a perturbation theory arising from a two-dimensional Hubbard model. The self-energy within the random phase approximation presents some inconsistencies; one of them is that its imaginary part presents more than one zero, which is a violation of the Luttinger theorem. We use a Bogolyubov transformation and within a spin density wave mean field, we recalculate the self-energy in the new ground state, and it is able to describe the Mott–Hubbard transition, satisfying the Luttinger condition.

Spin fluctuation effects in the normal state of Hubbard systems

Abstract We obtain and discuss the self-energy and the renormalized electronic structure of the normal state in strongly correlated electron systems within the pseudogap regime. The considered effective potentials are found from spin fluctuations within a Hubbard single band model. We find that the self-energy tends to violate the Luttinger theorem as the bandwidths are narrowed and also as the Hubbard U increases. This is an indication that a new fundamental state should be used to describe the system under these conditions. We have used an antiferromagnetic fundamental state and found that in this case the new self-energy does satisfy the Luttinger theorem.

Renormalized electronic structures of CeSi2, CeRu2 and CeAl2

Abstract The renormalized density of states of some Ce compounds is analyzed by considering self-energy effects. We study the influence of the hybridization introduced by the self-energy and how it can affect the shape of the characteristic lower, upper and middle-energy resonance.

Mott Transition in the Two-Dimensional Hubbard Model

We are interested in the description of the Mott-Hubbard transition from a perturbation theory arising from a two-dimensional Hubbard model. We calculate the self-energy within the random phase approximation and a double-Lorentzian as a non-interacting density of states. The paramagnetic ground state is unstable for realistic values of U, since the self-energy presents some inconsistencies ; one of them is that its imaginary part presents more than one zero, which is a violation of the Luttinger theorem. We use a Bogolyubov transformation and within a spin density wave mean field, the antiferromagnetic correlations of wave vector Q = (π/a,π/a) are included. We recalculate the self-energy in the new ground state and then it is able to describe the Mott-Hubbard transition, and the Luttinger theorem is satisfied.

Quasiparticle structure of Sr2RuO4

Abstract The non-copper layered perovskite, Sr 2 RuO 4 , is expected to be a very useful reference material for interpreting experiments on the high T c cuprate superconductors. A band structure calculation for Sr 2 RuO 4 is performed. Starting from the electronic structure determined in the local density formalism, the Dysons equation with self-energies arising from the Hubbard hamiltonian is solved by diagonalizing the Greens function in k -space. The density of states is obtained by considering the renormalization factor and the life-times of the quasiparticle states in each pole of the interacting system. This leads to modification of the density of states calculated in the local density formalism, and the results fit experimental data not only in the position of peaks, but also in their intensity and in the number of states at Fermi level.

Superconductivity by charge and spin fluctuations in strongly correlated systems

Abstract We obtain the effective potential from a screened coulombian interaction considering separately the interaction between fermions with parallel and antiparallel spins. In both cases we analyze the possibility of obtaining superconductivity.

Electronic structure of CeSi2

We calculate the electronic structure of CeSi2 using an energy-dependent potential, added to the local density Hamiltonian, arising from an approximation to the self-energy corresponding to a multiband Hubbard Hamiltonian.

Self-Energy Effects in the Electronic Structure of Ce Systems: Application to CeSi2 and CeAl2

We calculate the electronic structure of CeSi2 and CeAl2 using an energy-dependent potential arising from an approximation to the self-energy corresponding to a multiband Hubbard Hamiltonian. This potential is added to the local-density Hamiltonian and we determine the renormalized density of states. This density of states displays different peaks centred about −2.5 eV, ±0.3 eV, and 4 eV with respect to EF, corresponding to the characteristic f features. We analyse these results and compare them with the previous data and theoretical interpretations of the electronic structure of these interesting materials.

Electronic structure of the antiferromagnetic ground state of La2CuO4 beyond LDA+U method

Abstract With regard the Hubbard Hamiltonian, we use a Bogolyubov transformation and within a spin density wave mean field, where the antiferromagnetic correlations of wave vector Q =( π /a, π /a) are included. This gives a new energy spectrum that is calculated starting from the band structure of La2CuO4 determined in the local density formalism. We calculate the self-energy in this new ground state using the random phase approximation and a double Lorentzian as a non-interacting density of states. With this self-energy, Dysons equation is solved by diagonalizing the Greens function in k-space. The density of states is obtained by considering the renormalization factor and the lifetimes of the quasiparticle states in each pole. This leads to the splitting of the input density of states that is calculated in the local density formalism.

Quasiparticle structure and Fermi surface of Sr2RuO4

Abstract A quasiparticle structure calculation for Sr 2 RuO 4 is performed. Starting from the band structure determined in the local density formalism, the Dysons equation with self-energies arising from the Hubbard Hamiltonian, is solved by diagonalizing the Greens function in k -space. The density of states is obtained by considering the renormalization factor and the lifetimes of the quasiparticle states. We also obtain the Fermi surface without and with the inclusion of the strong correlations effects.