Effect of hybridization on the magnetic properties of correlated two-band metals

The magnetic properties of transition-like metals are discussed within the single site approximation, which is a picture to take into account electron correlations. The metal is described by two hybridized bands one of which includes Coulomb correlation. The presented results indicate that ferromagnetism arises for adequate values of hybridization (V), correlation (U) and occupation number($n_{\sigma}$). Some similarities with Dynamical Mean-Field Theory (DMFT) are indicated.Comment: 3 pages, 3 figures, presented at the 53rd MMM08 conference in Austin, 200

Pseudogap and the specific heat of high TcT_c superconductors

The specific heat of a two dimensional repulsive Hubbard model with local interaction is investigated. We use the two-pole approximation which exhibits explicitly important correlations that are sources of the pseudogap anomaly. The interplay between the specific heat and the pseudogap is the main focus of the present work. Our self consistent numerical results show that above the occupation $n_T\approx 0.85$, the specific heat starts to decrease due to the presence of a pseudogap in the density of states. We have also observed a two peak structure in the specific heat. Such structure is robust with respect to the Coulomb interaction $U$ but it is significantly affected by the occupation $n_T$. A detailed study of the two peak structure is carried out in terms of the renormalized quasi-particle bands. The role of the second nearest neighbor hopping on the specific heat behavior and on the pseudogap, is extensively discussed.Comment: 6 pages, 6 figures, accepted for publication in Solid State Communication

Specific heat of a non-local attractive Hubbard model

The specific heat of an attractive (interaction $G<0$) non-local Hubbard model is investigated. We use a two-pole approximation which leads to a set of correlation functions. In particular, the correlation function $\ $plays an important role as a source of anomalies in the normal state of the model. Our results show that for a giving range of$G$and$\delta$where$\delta=1-n_T$($n_T=n_{\uparrow}+n_{\downarrow}$), the specific heat as a function of the temperature presents a two peak structure. Nevertehelesss, the presence of a pseudogap on the anti-nodal points$(0,\pm\pi)$and$(\pm\pi,0)$ eliminates the two peak structure, the low temperature peak remaining. The effects of the second nearest neighbor hopping on the specific heat are also investigated.Comment: 5 pages, 7 figure

Cross effect of Coulomb correlation and hybridization in the occurrence of ferromagnetism in two shifted band transition metals

In this work we discuss the occurrence of ferromagnetism in transition-like metals. The metal is represented by two hybridized($V$) and shifted $(\epsilon_s$) bands one of which includes Hubbard correlation whereas the other is uncorrelated. The starting point is to transform the original Hamiltonian into an effective one. Only one site retains the full correlation (U) while in the others the correlations are represented by an effective field, the self-energy(single-site approximation). This field is self-consistently determined by imposing the translational invariance of the problem. Thereby one gets an exchange split quasi-particle density of states and then an electron-spin polarization for some values of the parameters $(U,V, \alpha, \epsilon_s)$, $\alpha$ being the ratio of the effective masses of the two bands and of the occupation number $n$.Comment: 4 pages, 10 figure