L. Craco — Page 3 | Searcharxiv

arXiv2000

Role of Orbital Degeneracy in Double Exchange Systems

We investigate the role of orbital degeneracy in the double exchange (DE) model. In the $J_{H}\to\infty$ limit, an effective generalized ``Hubbard'' model incorporating orbital pseudospin degrees of freedom is derived. The model possesses an exact solution in one- and in infinite dimensions. In 1D, the metallic phase off ``half-filling'' is a Luttinger liquid with pseudospin-charge separation. Using the $d=\infty$ solution for our effective model, we show how many experimental observations for the well-doped ($x\simeq 0.3$) three-dimensional manganites $La_{1-x}Sr_{x}MnO_{3}$ can be qualitatively explained by invoking the role of orbital degeneracy in the DE model.

cond-mat.str-el↗

arXiv1999

Disordered Hubbard model in $d=\infty$

We investigate the effects of static, diagonal disorder in the $d=\infty$ Hubbard model by treating the dynamical effects of local Hubbard correlations and disorder on an equal footing. This is achieved by a proper combination of the iterated perturbation theory and the coherent potential approximation. Within the paramagnetic phase, we find that the renormalized Fermi liquid metal phase of the pure Hubbard model is stable against disorder for small disorder strengths. With increasing disorder, strong resonant scattering effects destroy low-energy Fermi liquid coherence, leading to an {\it incoherent} metallic non-FL state off half-filling. Finally, for large enough disorder, a {\it continuous} transition to the Mott-Anderson insulating phase occurs. The nature of the non-FL metallic phase, as well as the effects of the low energy coherence (incoherence) on optical conductivity and electronic Raman spectra, are considered in detail.

cond-mat.str-el↗