Pedro A. Orellana

Kondo effect and bistability in a double quantum dot

We study theoretically the out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime. We model the system by means of a two-impurity Anderson Hamiltonian. The transport properties are characterized by Kondo effect properties, however, superimposed on them, and the system possesses nonlinear bistability behavior.

Transport properties of graphene quantum dots

In this work we present a theoretical study of transport properties of a double crossbar junction composed by segments of graphene ribbons with different widths forming a graphene quantum dot structure. The systems are described by a single-band tight binding Hamiltonian and the Greens function formalism using real space renormalization techniques. We show calculations of the local density of states, linear conductance and I-V characteristics. Our results depict a resonant behavior of the conductance in the quantum dot structures which can be controlled by changing geometrical parameters such as the nanoribbon segments widths and relative distance between them. By applying a gate voltage on determined regions of the structure, it is possible to modulate the transport response of the systems. We show that negative differential resistance can be obtained for low values of gate and bias voltages applied.

Suppression of Kondo screening by the Dicke effect in multiple quantum dots

Department of Physics and Astronomy, and Nanoscale and Quantum Phenomena Institute,Ohio University, Athens, Ohio 45701-2979(Dated: September 21, 2010)The interplay between the coupling of an interacting quantum dot to a conduction band and itsconnection to localized levels has been studied in a triple quantum dot arrangement. The electronicDicke effect, resulting from quasi-resonant states of two side-coupled non-interacting quantum dots,is found to produce important effects on the Kondo resonance of the interacting dot. We studyin detail the Kondo regime of the system by applying a numerical renormalization group analysisto a finite-U multi-impurity Anderson Hamiltonian model. We find an extreme narrowing of theKondo resonance, as the single-particle levels of the side dots are tuned towards the Fermi level and“squeeze” the Kondo resonance, accompanied by a strong drop in the Kondo temperature, due tothe presence of a supertunneling state. Further, we show that the Kondo temperature vanishes inthe limit of the Dicke effect of the structure. By analyzing the magnetic moment and entropy ofthe three-dot cluster versus temperature, we identify a different local singlet that competes with theKondo state, resulting in the eventual suppression of the Kondo temperature and strongly affectingthe spin correlations of the structure. We further show that system asymmetries in couplings, levelstructure or due to Coulomb interactions, result in interesting changes in the spectral function nearthe Fermi level. These strongly affect the Kondo temperature and the linear conductance of thesystem.

Kondo and Dicke effect in quantum dots side coupled to a quantum wire

Electron tunneling through quantum dots side coupled to a quantum wire, in equilibrium and nonequilibrium Kondo regime, is studied. The mean-field finite-

Negative differential conductance induced by electronic correlation in a double quantum dot molecule

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Kondo effect in side coupled double quantum-dot molecule

slave-boson formalism is used to obtain the solution of the problem. We have found that the transmission spectrum shows a structure with two antiresonances localized at the renormalized energies of the quantum dots. The density of states (DOS) of the system shows that when the Kondo correlations are dominant there are two Kondo regimes with its own Kondo temperature. The above behavior of the DOS can be explained by quantum interference in the transmission through the two different resonance states of the quantum dots coupled to common leads. This result is analogous to the Dicke effect in optics. We investigate the many-body Kondo states as a function of the parameters of the system.

Tristability in a non-equilibrium double-quantum-dot in the Kondo regime

Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule side coupled to a quantum wire, under the effect of a finite external potential is studied. We found that

Electronic transport of folded graphene nanoribbons

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Optoelectronic Properties of Van Der Waals Hybrid Structures: Fullerenes on Graphene Nanoribbons

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Kondo effect in a double quantum-dot molecule under the effect of an electric and magnetic field

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