1,714 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
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
Origins of conductance anomalies in a p-type GaAs quantum point contact
Low temperature transport measurements on a p-GaAs quantum point contact are
presented which reveal the presence of a conductance anomaly that is markedly
different from the conventional `0.7 anomaly'. A lateral shift by asymmetric
gating of the conducting channel is utilized to identify and separate different
conductance anomalies of local and generic origins experimentally. While the
more generic 0.7 anomaly is not directly affected by changing the gate
configuration, a model is proposed which attributes the additional conductance
features to a gate-dependent coupling of the propagating states to localized
states emerging due to a nearby potential imperfection. Finite bias
conductivity measurements reveal the interplay between the two anomalies
consistently with a two-impurity Kondo model
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