Kondo Effect and Conductance of Nanocontacts with Magnetic Impurities (original) (raw)
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Coherent electronic transport and Kondo resonance in magnetic nanostructures
Physical Review B, 2003
We consider coherent electronic transport between two ferromagnetic electrodes separated either by a metallic nanoparticle or by a conducting molecule. Correlations between electrons with opposite spins lead to the Kondo resonance, which manifests a formation of the singlet state. Although tunnelling rates for electrons with opposite spin orientations are different the conductance reaches the unitary limit in the Kondo regime. We predict a negative magnetoresistance effect, which can be observed for asymmetric magnetic junctions.
Coherent transport in extremely underdoped Nd 1.2 Ba 1.8 Cu 3 O z nanostructures
New Journal of Physics, 2012
Proximity-effect and resistance magneto-fluctuation measurements in submicron Nd 1.2 Ba 1.8 Cu 3 O z (NBCO) nano-loops are reported to investigate coherent charge transport in the non-superconducting state. We find an unexpected inhibition of Cooper pair transport, and a destruction of the induced superconductivity, by lowering the temperature from 6 K to 250 mK. This effect is accompanied by a significant change in the conductancevoltage characteristics and the zero bias conductance response to the magnetic field, pointing to the activation of a strong pair-breaking mechanism at lower temperature. The data are discussed in the framework of mesoscopic effects specific to superconducting nanostructures, proximity effect and high temperature superconductivity.
1D Kondo Lattice with coulomb interaction: Application to Cu(Pc)I
Synthetic Metals, 1989
The one-dimensional Kondo lattice problem of a conductinE chain exchanEecoupled to a localized spin chain is revisited. We look at the magnetic susceptibility and the low temperature state and consider the effect of Coulomb interactions within the conductinE chain. We correlate our findings to the measurements on Cu(Pc)I, an organic conductor in which the localized moments are imbedded within the conductinE chains. We conclude that there is no Kondo effect. The susceptibility can be very well reproduced by assuminE a direct interaction of 4.55 K between localized moments, a local rnocBent-conductinE electron exchanEe of 35.7 K, a Coulomb enhanced power exponent of ], and a transition tem~rature of 8 K to an RKKY state. INTROIX~ION Recent measurements on the or~panic conductor {phthalocyaninato}copper iodide [1], or Cu(Pc)I for short, have revealed that this quasi-onedimensional (ID) charge transfer salt has local spin ~ magnetic moments on the Cu ÷z which interact stronEly with the conduction holes on the same molecules. This may well be a rare example of a 1D Kondo lattice [2a]. Our objective was thus to study this specific model and try to see if the observed magnetic susceptibility and the suggested "transition" to a Kondo state at 8 K were compatible with it. We shall derive the static magnetic susceptibility and examine the spin density wave instability resulting from the well known Ruderman-I
Transport in coupled quantum dots: Kondo effect versus antiferromagnetic correlation
Physical Review B, 2000
The interplay between the Kondo effect and the inter-dot magnetic interaction in a coupled-dot system is studied. An exact result for the transport properties at zero temperature is obtained by diagonalizing a cluster, composed by the double-dot and its vicinity, which is connected to leads. It is shown that the system goes continuously from the Kondo regime to an anti-ferromagnetic state as the inter-dot interaction is increased. The conductance, the charge at the dots and the spin-spin correlation are obtained as a function of the gate potential.
Kondo Effect in the Presence of Magnetic Impurities
Physical Review Letters, 2006
We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to a RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.
Physical Review B, 2005
We investigate the nonequilibrium transport properties of a three-terminal quantum dot in the strongly interacting limit. At low temperatures, a Kondo resonance arises from the antiferromagnetic coupling between the localized electron in the quantum dot and the conduction electrons in source and drain leads. It is known that the local density of states is accessible through the differential conductance measured at the (weakly coupled) third lead. Here, we consider the multiterminal current-current correlations (shot noise and cross correlations measured at two different terminals). We discuss the dependence of the current correlations on a number of external parameters: bias voltage, magnetic field and magnetization of the leads. When the Kondo resonance is split by fixing the voltage bias between two leads, the shot noise shows a nontrivial dependence on the voltage applied to the third lead. We show that the cross correlations of the current are more sensitive than the conductance to the appearance of an external magnetic field. When the leads are ferromagnetic and their magnetizations point along opposite directions, we find a reduction of the cross correlations. Moreover, we report on the effect of dephasing in the Kondo state for a two-terminal geometry when the third lead plays the role of a fictitious voltage probe.
The Kondo effect in the presence of magnetic impurities
2006
We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to an RKKY interaction (I) between the spin of the dot and the static spins of the impurities. Both ferromagnetic and anti- ferromagnetic interactions have been observed in different samples. A magnetic field restores the single Kondo peak in the case of an anti-ferromagnetic RKKY interaction, whereas the splitting is enhanced in the case of ferromagnetic interaction. A gate electrode can change the relative interaction strength TK/I. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.
Kondo effect in a metal with correlated conduction electrons: Diagrammatic approach
Physical Review B, 2003
The large-degeneracy expansion for dilute magnetic alloys is extended to account for conduction electrons interactions. Particular attention is paid to the renormalization of the hybridization vertex which affects the low-energy excitations. As a first example, we calculate the enhanced characteristic energy kBT0 in the limit of weakly correlated conduction electrons. The metallic regime with strongly correlated electrons is discussed.
The Kondo effect in ferromagnetic atomic contacts
Nature, 2009
Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature 1. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system;this appears as a Fano-Kondo resonance 2 in the conductance characteristics as observed in other artificial nanostructures 3,