1,613 research outputs found
Phonon-assisted and magnetic field induced Kondo tunneling in single molecular devices
We consider the Kondo tunneling induced by multiphonon emission/absorption
processes in magnetic molecular complexes with low-energy singlet-triplet spin
gap and show that the number of assisting phonons may be changed by varying the
Zeeman splitting of excited triplet state. As a result, the structure of
multiphonon Kondo resonances may be scanned by means of magnetic field tuning.Comment: 7 pages, 6 figures. Shortened version of this paper will be published
in the Proceedings of the International Conference "Phonons2007" (J. Phys:
Conf. Series
Spatially dependent Kondo effect in Quantum Corrals
We study the Kondo screening of a single magnetic impurity inside a
non-magnetic quantum corral located on the surface of a metallic host system.
We show that the spatial structure of the corral's eigenmodes lead to a
spatially dependent Kondo effect whose signatures are spatial variations of the
Kondo temperature, . Moreover, we predict that the Kondo screening is
accompanied by the formation of multiple Kondo resonances with characteristic
spatial patterns. Our results open new possibilities to manipulate and explore
the Kondo effect by using quantum corrals.Comment: 4 pages 5 figure
Strongly Inhomogeneous Phases and Non-Fermi Liquid Behavior in Randomly Depleted Kondo Lattices
We investigate the low-temperature behavior of Kondo lattices upon random
depletion of the local -moments, by using strong-coupling arguments and
solving SU() saddle-point equations on large lattices. For a large range of
intermediate doping levels, between the coherent Fermi liquid of the dense
lattice and the single-impurity Fermi liquid of the dilute limit, we find
strongly inhomogeneous states that exhibit distinct non-Fermi liquid
characteristics. In particular, the interplay of dopant disorder and strong
interactions leads to rare weakly screened moments which dominate the bulk
susceptibility. Our results are relevant to compounds like Ce_{x}La_{1-x}CoIn_5
and Ce_{x}La_{1-x}Pb_3Comment: 4 pages, 5 figure
Defects in Heavy-Fermion Materials: Unveiling Strong Correlations in Real Space
Complexity in materials often arises from competing interactions at the
atomic length scale. One such example are the strongly correlated heavy-fermion
materials where the competition between Kondo screening and antiferromagnetic
ordering is believed to be the origin of their puzzling non-Fermi-liquid
properties. Insight into such complex physical behavior in strongly correlated
electron systems can be gained by impurity doping. Here, we develop a
microscopic theoretical framework to demonstrate that defects implanted in
heavy-fermion materials provide an opportunity for unveiling competing
interactions and their correlations in real space. Defect-induced perturbations
in the electronic and magnetic correlations possess characteristically
different spatial patterns that can be visualized via their spectroscopic
signatures in the local density of states or non-local spin susceptibility.
These real space patterns provide insight into the complex electronic structure
of heavy-fermion materials, the light or heavy character of the perturbed
states, and the hybridization between them. The strongly correlated nature of
these materials also manifests itself in highly non-linear quantum interference
effects between defects that can drive the system through a first-order phase
transition to a novel inhomogeneous ground state.Comment: 11 pages, 7 figure
Phase diagram, energy scales and nonlocal correlations in the Anderson lattice model
We study the Anderson lattice model with one f-orbital per lattice site as
the simplest model which describes generic features of heavy fermion materials.
The resistivity and magnetic susceptibility results obtained within dynamical
mean field theory (DMFT) for a nearly half-filled conduction band show the
existence of a single energy scale which is similar to the single ion
Kondo temperature . To determine the importance of inter-site
correlations, we have also solved the model within cellular DMFT (CDMFT) with
two sites in a unit cell. The antiferromagnetic region on the phase diagram is
much narrower than in the single-site solution, having a smaller critical
hybridization and N\'eel temperature . At temperatures above
the nonlocal correlations are small, and the DMFT paramagnetic solution is in
this case practically exact, which justifies the ab initio LDA+DMFT approach in
theoretical studies of heavy fermions. Strong inter-site correlations in the
CDMFT solution for , however, indicate that they have to be properly
treated in order to unravel the physical properties near the quantum critical
point.Comment: 10 page
Two-channel Kondo physics in two-impurity Kondo models
We consider the non-Fermi liquid quantum critical state of the spin-S
two-impurity Kondo model, and its potential realization in a quantum dot
device. Using conformal field theory (CFT) and the numerical renormalization
group (NRG), we show the critical point to be identical to that of the
two-channel Kondo model with additional potential scattering, for any spin-S.
Distinct conductance signatures are shown to arise as a function of device
asymmetry; with the `smoking gun' square-root behavior, commonly believed to
arise at low-energies, dominant only in certain regimes.Comment: 4.5 pages (with 3 figures) + 9 pages (with 4 figures) supplementary
materia
Theory of Fano-Kondo effect in quantum dot systems: temperature dependence of the Fano line shapes
The Fano-Kondo effect in zero-bias conductance is studied based on a
theoretical model for the T-shaped quantum dot by the finite temperature
density matrix renormalization group method. The modification of the two Fano
line shapes at much higher temperatures than the Kondo temperature is also
investigated by the effective Fano parameter estimated as a fitting parameter.Comment: 2 pages, 2 figures, the proceeding of SCES'0
Kondo behavior in the asymmetric Anderson model: Analytic approach
The low-temperature behavior of the asymmetric single-impurity
Anderson model is studied by diagrammatic methods resulting in analytically
controllable approximations. We first discuss the ways one can simplify parquet
equations in critical regions of singularities in the two-particle vertex. The
scale vanishing at the critical point defines the Kondo temperature at which
the electron-hole correlation function saturates. We show that the Kondo
temperature exists at any filling of the impurity level. A quasiparticle
resonance peak in the spectral function, however, forms only in almost
electron-hole symmetric situations. We relate the Kondo temperature with the
width of the resonance peak. Finally we discuss the existence of satellite
Hubbard bands in the spectral function.Comment: REVTeX4, 11 pages, 5 EPS figure
The Realization of Artificial Kondo Lattices in Nanostructured Arrays
The interplay of magnetic energies in a Kondo lattice is the underlying
physics of a heavy fermion system. Creating an artificial Kondo lattice system
by localizing the moments in an ordered metallic array provides a prototype
system to tune and study the energetic interplay while avoiding the
complications introduced by random alloying of the material. In this article,
we create a Kondo lattice system by fabricating a hexagonally ordered
nanostructured array using niobium as the host metal and cobalt as the magnetic
constituent. Electrical transport measurements and magnetoresistivity
measurements of these artificial lattices show that the competing exchange
coupling properties can be easily tuned by controlling the impurity percentage.
These artificial Kondo lattice systems enable the exploration of an artificial
superconductor which should lead to a deep understanding of the role of
magnetism in unconventional superconductors.Comment: Artificial Magnetic Crystal
Magnetic phases in the correlated Kondo-lattice model
We study magnetic ordering of an extended Kondo-lattice model including an
additional on-site Coulomb interaction between the itinerant states. The model
is solved in the dynamical mean-field theory using Wilson's numerical
renormalization group approach as impurity solver. For a bipartite lattice we
find at half filling the expected antiferromagnetic phase. Upon doping this
phase is gradually suppressed and hints towards phase separation are observed.
For large doping the model exhibits ferromagnetism, the appearance of which can
at first sight be explained by Rudermann-Kittel-Kasuya-Yosida interaction.
However, for large values of the Kondo coupling significant differences to
a simple Rudermann-Kittel-Kasuya-Yosida picture can be found. We furthermore
observe signs of quantum critical points for antiferromagnetic Kondo coupling
between the local spins and band states
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