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Between the nano- and micrometre scales, the collective behaviour of matter
can give rise to startling emergent properties that hint at the nexus between
biology and physics.Comment: Archival copy of Nature Connections Articl
Electron Cotunneling into a Kondo Lattice
Motivated by recent experimental interest in tunneling into heavy electron
materials, we present a theory for electron tunneling into a Kondo lattice. The
passage of an electron into the Kondo lattice is accompanied by a simultaneous
spin flip of the localized moments via cotunneling mechanism. We compute the
tunneling current with the large- mean field theory. In the absence of
disorder, differential tunneling conductance exhibits two peaks separated by
the hybridization gap. Disorder effects lead to the smearing of the gap
resulting in a Fano lineshape.Comment: 4 pages, 2 eps figure
Transport anomalies in a simplified model for a heavy electron quantum critical point
We discuss the transport anomalies associated with the development of heavy
electrons out of a neutral spin fluid using the large-N treatment of the
Kondo-Heisenberg lattice model. At the phase transition in this model the spin
excitations suddenly acquire charge. The Higgs process by which this takes
place causes the constraint gauge field to loosely ``lock'' together with the
external, electromagnetic gauge field. From this perspective, the heavy fermion
phase is a Meissner phase in which the field representing the difference
between the electromagnetic and constraint gauge field, is excluded from the
material. We show that at the transition into the heavy fermion phase, both the
linear and the Hall conductivity jump together. However, the Drude weight of
the heavy electron fluid does not jump at the quantum critical point, but
instead grows linearly with the distance from the quantum critical point,
forming a kind of ``gossamer'' Fermi-liquid.Comment: 15 pages, 3 figures. Small change in references in v
Itinerant and localized states in strongly correlated systems by a modified mean-field slave-boson approach
The standard mean field slave-boson solution for the infinite- Hubbard
model is revised. A slightly modified version is proposed which includes
properly the incoherent contribution of the localized states. In contrast to
the standard mean field result, this new proposed solution defines a unique
spectral function to be used in the calculation of local and not local
quantities, and satisfies the correct thermodynamic relations. The same
approach is applied also to the mean field approximation in terms of Hubbard
operators. As a byproduct of this analysis, Luttinger's theorem is shown to be
fulfilled in a natural way.Comment: 2 eps figure enclosed, IJMP B style, accepted for publication on Int.
Journ. Mod. Phys.
Kondo resonance narrowing in d- and f-electron systems
By developing a simple scaling theory for the effect of Hund's interactions
on the Kondo effect, we show how an exponential narrowing of the Kondo
resonance develops in magnetic ions with large Hund's interaction. Our theory
predicts an exponential reduction of the Kondo temperature with spin S of the
Hund's coupled moment, a little-known effect first observed in d-electron
alloys in the 1960's, and more recently encountered in numerical calculations
on multi-band Hubbard models with Hund's interactions. We discuss the
consequences of Kondo resonance narrowing for the Mott transition in d-band
materials, particularly iron pnictides, and the narrow ESR linewidth recently
observed in ferromagnetically correlated f-electron materials.Comment: 4 pages, 3 figure
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D.
Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the
phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that
thermodynamic and transport properties of Kondo lattices below coherence
temperature can be very successfully described in terms of a two-fluid model,
with Kondo impurity and heavy electron Fermi liquid contributions. We analyze
thermodynamic properties of Kondo lattices using 1/N slave boson treatment of
the periodic Anderson model and show that these two contributions indeed arise
below the coherence temperature. We find that the Kondo impurity contribution
to thermodynamics corresponds to thermal excitations into the flat portion of
the energy spectrum.Comment: 7 pages, 2 figure
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