2,037 research outputs found
Suppression of Shot Noise in Quantum Point Contacts in the "0.7" Regime
Experimental investigations of current shot noise in quantum point contacts
show a reduction of the noise near the 0.7 anomaly. It is demonstrated that
such a reduction naturally arises in a model proposed recently to explain the
characteristics of the 0.7 anomaly in quantum point contacts in terms of a
quasi-bound state, due to the emergence of two conducting channels. We
calculate the shot noise as a function of temperature, applied voltage and
magnetic field, and demonstrate an excellent agreement with experiments. It is
predicted that with decreasing temperature, voltage and magnetic field, the dip
in the shot noise is suppressed due to the Kondo effect.Comment: 4 pages, 1 figur
Evidence for localization and 0.7 anomaly in hole quantum point contacts
Quantum point contacts implemented in p-type GaAs/AlGaAs heterostructures are
investigated by low-temperature electrical conductance spectroscopy
measurements. Besides one-dimensional conductance quantization in units of
a pronounced extra plateau is found at about which
possesses the characteristic properties of the so-called "0.7 anomaly" known
from experiments with n-type samples. The evolution of the 0.7 plateau in high
perpendicular magnetic field reveals the existence of a quasi-localized state
and supports the explanation of the 0.7 anomaly based on self-consistent charge
localization. These observations are robust when lateral electrical fields are
applied which shift the relative position of the electron wavefunction in the
quantum point contact, testifying to the intrinsic nature of the underlying
physics.Comment: 4.2 pages, 3 figure
Phase switching in a voltage-biased Aharonov-Bohm interferometer
Recent experiment [Sigrist et al., Phys. Rev. Lett. {\bf 98}, 036805 (2007)]
reported switches between 0 and in the phase of Aharonov-Bohm
oscillations of the two-terminal differential conductance through a two-dot
ring with increasing voltage bias. Using a simple model, where one of the dots
contains multiple interacting levels, these findings are explained as a result
of transport through the interferometer being dominated at different biases by
quantum dot levels of different "parity" (i.e. the sign of the overlap integral
between the dot state and the states in the leads). The redistribution of
electron population between different levels with bias leads to the fact that
the number of switching events is not necessarily equal to the number of dot
levels, in agreement with experiment. For the same reason switching does not
always imply that the parity of levels is strictly alternating. Lastly, it is
demonstrated that the correlation between the first switching of the phase and
the onset of the inelastic cotunneling, as well as the sharp (rather than
gradual) change of phase when switching occurs, give reason to think that the
present interpretation of the experiment is preferable to the one based on
electrostatic AB effect.Comment: 12 pages, 9 figure
Spin-Orbit Assisted Variable-Range Hopping in Strong Magnetic Fields
It is shown that in the presence of strong magnetic fields, spin-orbit
scattering causes a sharp increase in the effective density of states in the
variable-range hopping regime when temperature decreases. This effect leads to
an exponential enhancement of the conductance above its value without
spin-orbit scattering. Thus an experimental study of the hopping conductivity
in a fixed, large magnetic field, is a sensitive tool to explore the spin-orbit
scattering parameters in the strongly localized regime.Comment: 9 pages + 2 figures (enclosed), Revte
Generalized conductance sum rule in atomic break junctions
When an atomic-size break junction is mechanically stretched, the total
conductance of the contact remains approximately constant over a wide range of
elongations, although at the same time the transmissions of the individual
channels (valence orbitals of the junction atom) undergo strong variations. We
propose a microscopic explanation of this phenomenon, based on Coulomb
correlation effects between electrons in valence orbitals of the junction atom.
The resulting approximate conductance quantization is closely related to the
Friedel sum rule.Comment: 4 pages, 1 figure, appears in Proceedings of the NATO Advanced
Research Workshop ``Size dependent magnetic scattering'', Pecs, Hungary, May
28 - June 1, 200
Non-collinear magnetoconductance of a quantum dot
We study theoretically the linear conductance of a quantum dot connected to
ferromagnetic leads. The dot level is split due to a non-collinear magnetic
field or intrinsic magnetization. The system is studied in the non-interacting
approximation, where an exact solution is given, and, furthermore, with Coulomb
correlations in the weak tunneling limit. For the non-interacting case, we find
an anti-resonance for a particular direction of the applied field,
non-collinear to the parallel magnetization directions of the leads. The
anti-resonance is destroyed by the correlations, giving rise to an interaction
induced enhancement of the conductance. The angular dependence of the
conductance is thus distinctly different for the interacting and
non-interacting cases when the magnetizations of the leads are parallel.
However, for anti-parallel lead magnetizations the interactions do not alter
the angle dependence significantly.Comment: 7 pages, 7 figure
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