773 research outputs found
Mesoscopic transport beyond linear response
We present an approach to steady-state mesoscopic transport based on the
maximum entropy principle formulation of nonequilibrium statistical mechanics.
Our approach is not limited to the linear response regime. We show that this
approach yields the quantization observed in the integer quantum Hall effect at
large currents, which until now has been unexplained. We also predict new
behaviors of non-local resistances at large currents in the presence of dirty
contacts.Comment: 14 pages plus one figure (with an insert) (post-script codes
appended), RevTeX 3.0, UCF-CM-93-004 (Revised
A new perturbation treatment applied to the transport through a quantum dot
Resonant tunnelling through an Anderson impurity is investigated by employing
a new perturbation scheme at nonequilibrium. This new approach gives the
correct weak and strong coupling limit in by introducing adjustable
parameters in the self-energy and imposing self-consistency of the occupation
number of the impurity. We have found that the zero-temperature linear response
conductance agrees well with that obtained from the exact sum rule. At finite
temperature the conductance shows a nonzero minimum at the Kondo valley, as
shown in recent experiments. The effects of an applied bias voltage on the
single-particle density of states and on the differential conductances are
discussed for Kondo and non-Kondo systems.Comment: 4 pages, 4 figures, submitted to PRB-Rapid Comm. Email addresses
[email protected], [email protected]
Mesoscopic Kondo Effect in an Aharonov-Bohm Ring
An interacting quantum dot inserted in a mesoscopic ring is investigated. A
variational ansatz is employed to describe the ground state of the system in
the presence of the Aharonov-Bohm flux. It is shown that, for even number of
electrons with the energy level spacing smaller than the Kondo temperature, the
persistent current has a value similar to that of a perfect ring with the same
radius. On the other hand, for a ring with odd number electrons, the persistent
current is found to be strongly suppressed compared to that of an ideal ring,
which implies the suppression of the Kondo-resonant transmission. Various
aspects of the Kondo-assisted persistent current are discussed.Comment: 4 pages Revtex, 4 Postscript figures, final version to appear in
Phys. Rev. Lett. 85, No.26 (Dec. 25, 2000
Theory of Scanning Tunneling Spectroscopy of a Magnetic Adatom on a Metallic Surface
A comprehensive theory is presented for the voltage, temperature, and spatial
dependence of the tunneling current between a scanning tunneling microscope
(STM) tip and a metallic surface with an individual magnetic adatom. Modeling
the adatom by a nondegenerate Anderson impurity, a general expression is
derived for a weak tunneling current in terms of the dressed impurity Green
function, the impurity-free surface Green function, and the tunneling matrix
elements. This generalizes Fano's analysis to the interacting case. The
differential-conductance lineshapes seen in recent STM experiments with the tip
directly over the magnetic adatom are reproduced within our model, as is the
rapid decay, \sim 10\AA, of the low-bias structure as one moves the tip away
from the adatom. With our simple model for the electronic structure of the
surface, there is no dip in the differential conductance at approximately one
lattice spacing from the magnetic adatom, but rather we see a resonant
enhancement. The formalism for tunneling into small clusters of magnetic
adatoms is developed.Comment: 12 pages, 9 figures; to appear in Phys. Rev.
Nonbackscattering Contribution to the Weak Localization
We show that the enhancement of backscattering responsible for the weak
localization is accompanied by reduction of the scattering in other directions.
A simple quasiclassical interpretation of this phenomenon is presented in terms
of a small change in the effective differential cross-section for a single
impurity. The reduction of the scattering at the arbitrary angles leads to the
decrease of the quantum correction to the conductivity. Within the diffusion
approximation this decrease is small, but it should be taken into account in
the case of a relatively strong magnetic field when the diffusion approximation
is not valid.Comment: 18 pages, 6 figures, Submitted to PR
Effect of the Coulomb repulsion on the {\it ac} transport through a quantum dot
We calculate in a linear response the admittance of a quantum dot out of
equilibrium. The interaction between two electrons with opposite spins
simultaneously residing on the resonant level is modeled by an Anderson
Hamiltonian. The electron correlations lead to the appearence of a new feature
in the frequency dependence of the conductance. For certain parameter values
there are two crossover frequencies between a capacitive and an inductive
behavior of the imaginary part of the admittance. The experimental implications
of the obtained results are briefly discussed.Comment: 13 pages, REVTEX 3.0, 2 .ps figures from [email protected],
NUB-308
Modified Perturbation Theory Applied to Kondo-Type Transport through a Quantum Dot under a Magnetic Field
Linear conductance through a quantum dot is calculated under a finite
magnetic field using the modified perturbation theory. The method is based on
the second-order perturbation theory with respect to the Coulomb repulsion, but
the self-energy is modified to reproduce the correct atomic limit and to
fulfill the Friedel sum rule exactly. Although this method is applicable only
to zero temperature in a strict sense, it is approximately extended to finite
temperatures. It is found that the conductance near electron-hole symmetry is
suppressed by the application of the magnetic field at low temperatures.
Positive magnetoconductance is observed in the case of large electron-hole
asymmetry.Comment: 4pages, 5 figure
Interplay between Coulomb Blockade and Resonant Tunneling studied by the Keldysh Green's Function Method
A theory of tunneling through a quantum dot is presented which enables us to
study combined effects of Coulomb blockade and discrete energy spectrum of the
dot. The expression of tunneling current is derived from the Keldysh Green's
function method, and is shown to automatically satisfy the conservation at DC
current of both junctions.Comment: 4 pages, 3 figures(mail if you need), use revtex.sty, error
corrected, changed titl
Finite-Size Bosonization of 2-Channel Kondo Model: a Bridge between Numerical Renormalization Group and Conformal Field Theory
We generalize Emery and Kivelson's (EK) bosonization-refermionization
treatment of the 2-channel Kondo model to finite system size and on the EK-line
analytically construct its exact eigenstates and finite-size spectrum. The
latter crosses over to conformal field theory's (CFT) universal
non-Fermi-liquid spectrum (and yields the most-relevant operators' dimensions),
and further to a Fermi-liquid spectrum in a finite magnetic field. Our approach
elucidates the relation between bosonization, scaling techniques, the numerical
renormalization group (NRG) and CFT. All CFT's Green's functions are recovered
with remarkable ease from the model's scattering states.Comment: 4 pages, 1 figure, Revte
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