378 research outputs found
Quantum interference effects in p-Si1−xGex quantum wells
Quantum interference effects, such as weak localization and electronelectron interaction (EEI), have been investigated in magnetic fields up to 11 T for hole gases in a set of Si1−xGex quantum wells with 0.13 < x < 0.95. The temperature dependence of the hole phase relaxation time has been extracted from the magneto-resistance between 35 mK and 10 K. The spin-orbit effects that can be described within the Rashba model were observed in low magnetic fields. A quadratic negative magneto-resistance was observed in strong magnetic fields, due to the EEI effect. The hole-phonon scattering time was determined from hole overheating in a strong magnetic field
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
Electron correlation resonances in the transport through a single quantum level
Correlation effects in the transport properties of a single quantum level
coupled to electron reservoirs are discussed theoretically using a
non-equilibrium Green functions approach. Our method is based on the
introduction of a second-order self-energy associated with the Coulomb
interaction that consistently eliminates the pathologies found in previous
perturbative calculations. We present results for the current-voltage
characteristic illustrating the different correlation effects that may be found
in this system, including the Kondo anomaly and Coulomb blockade. We finally
discuss the experimental conditions for the simultaneous observation of these
effects in an ultrasmall quantum dot.Comment: 4 pages (two columns), 3 figures under reques
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.
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
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
Exact non-equilibrium current from the partition function for impurity transport problems
We study the partition functions of quantum impurity problems in the domain
of complex applied bias for its relation to the non-equilibrium current
suggested by Fendley, Lesage and Saleur (cond-mat/9510055). The problem is
reformulated as a certain generalization of the linear response theory that
accomodates an additional complex variable. It is shown that the mentioned
relation holds in a rather generic case in the linear response limit, or under
certain condition out of equilibrium. This condition is trivially satisfied by
the quadratic Hamiltonians and is rather restrictive for the interacting
models. An example is given when the condition is violated.Comment: 10 pages, RevTex. Final extended versio
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
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
- …