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Kondo Effect (kondo + effect)

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Physics and Astronomy100%

Selected Abstracts

Kondo effect in oscillating molecules

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2009
Jernej Mravlje
Abstract We consider electronic transport through break-junctions bridged by a single molecule in the Kondo regime. We describe the system by a two-channel Anderson model. We take the tunneling matrix elements to depend on the position of the molecule. It is shown, that if the modulation of the tunneling by displacement is large, the potential confining the molecule to the central position between the leads is softened and the position of the molecule is increasingly susceptible to external perturbations that break the inversion symmetry. In this regime, the molecule is attracted to one of the leads and as a consequence the conductance is small. We argue on semi-classical grounds why the softening occurs and corroborate our findings by numerical examples obtained by Wilson's numerical renormalization group and Schönhammer,Gunnarsson's variational method (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Orbital Kondo effect and spin polarized transport through quantum dots

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
S. Lipi
Abstract The coherent spin dependent transport through a set of two capacitively coupled quantum dots placed in a magnetic field is considered within the equation of motion method. The magnetic field breaks the spin degeneracy. For special choices of gate voltages the dot levels are tuned to resonance and the orbital Kondo effect results. For different Zeemann splittings at the dots the Kondo resonance can be formed for only one spin channel. In this case the system operates as an efficient spin filter. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Aharonov,Bohm effect of a quantum ring in the Kondo regime

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
U. F. Keyser
Abstract We investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov,Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov,Bohm period explained by electron,electron interaction in our small quantum ring. [source]

Dynamical symmetries and quantum transport through nanostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2007
*Article first published online: 18 JUN 200, M. N. Kiselev
Abstract We discuss the manifestation of dynamical symmetries in quantum transport through nanostructures. The dynamical symmetry SO (4) manifested in the singlet-triplet excitations is shown to be responsible for several exotic effects in nano-devices: non-equilibrium Kondo effect in T-shape Double Quantum Dots, phonon-induced Kondo effect in transition-metal-organic complexes, Kondo shuttling in Nano-Electromechanical Single Electron Transistor. We consider the interplay between charge U (1) and spin SU (2) fluctuations in the vicinity of Stoner instability point and a non-monotonic behavior of a Tunneling Density of States in metallic quantum dots. The experiments showing important role of dynamical symmetries in nanostructures are briefly reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic impurities in small metal clusters

ANNALEN DER PHYSIK, Issue 9-10 2005
G.M. Pastor
Abstract Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods. The singlet-triplet spin gap ,E shows a remarkable dependence as a function of band-filling, cluster structure, and impurity position that can be interpreted in terms of the environment-specific conduction-electron spectrum. The low-energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite-temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite-size equivalent of the Kondo effect is identified and its structural dependence is discussed. [source]