arXiv subjects

T. Lobo

Publications and source records attributed to T. Lobo.

3 recordsLinked to original sources

arXiv2019

Carbon nanotube with pressure inducing pseudogaps: Kondo effect study

In this work we are interested to studying the Kondo effect present in a system with a $T$-shape ligation between a single-wall carbon nanotube (SWNT) and a magnetic impurity. The system has been studied under hydrostatic pressure and it was observed the opening of the gap in the density of states of the zigzag metallic tube. The pressure can be modeled by the Pierls instability and in this work we consider the out-of-plane distortion. A tight-binding approximation is used to calculate the SWNT Green's functions with hydrostatic pressure applied. We studied the disappearance of the Kondo peak as the gap opens. Moreover, we observed the strong influence of the pressure in the conductance curve that can be explained by the variation of Kondo peak height. The Kondo effect was reproduced with the atomic approach with $U\rightarrow\infty$ developed previously. Results of the electronic density of states and curves of the conductance are presented.

cond-mat.str-el↗

arXiv2010

Green's Functions for the Anderson model: the Atomic Approximation

We consider the cumulant expansion of the PAM employing the hybridization as perturbation (Phys. Rev. B 50, 17933 (1994)), and we obtain formally exact one-electron Green's functions (GF). These GF contain effective cumulants that are as difficult to calculate as the original GF, and the Atomic Approximation consists in substituting the effective cumulants by the ones that correspond to the atomic case, namely by taking a conduction band of zeroth width and local hybridization. This approximation has already been used for the case of infinite electronic repulsion U (Phys. Rev. B 62, 7882 (2000)), and here we extend the treatment to the case of finite U. The method can also be applied to the single impurity Anderson model (SIAM), and we give explicit expressions of the approximate GF both for the PAM and the SIAM.

cond-mat.str-el↗

arXiv2009

The atomic approach of the Anderson model for the U finite case: application to a quantum dot

In the present work we apply the atomic approach to the single impurity Anderson model (SIAM). A general formulation of this approach, that can be applied both to the impurity and to the lattice Anderson Hamiltonian, was developed in a previous work (arXiv:0903.0139v1 [cond-mat.str-el]). The method starts from the cumulant expansion of the periodic Anderson model (PAM), employing the hybridization as perturbation. The atomic Anderson limit is analytically solved and its sixteen eigenenergies and eigenstates are obtained. This atomic Anderson solution, which we call the (AAS), has all the fundamental excitations that generate the Kondo effect, and in the atomic approach is employed as a seed to generate the approximate solutions for finite U. The width of the conduction band is reduced to zero in the AAS, and we choose its position so that the Friedel sum rule (FSR) be satisfied, close to the chemical potential. We perform a complete study of the density of states of the SIAM in all the relevant range of parameters: the empty dot, the intermediate valence (IV-regime),the Kondo and the magnetic regime. In the Kondo regime we obtain a density of states that characterizes well the structure of the Kondo peak. To shown the usefulness of the method we have calculated the conductance of a quantum dot, side coupled to a conduction band.

cond-mat.str-el↗