8,713 research outputs found
Strong Tunneling and Coulomb Blockade in a Single-Electron Transistor
We have developed a detailed experimental study of a single-electron
transistor in a strong tunneling regime. Although weakened by strong charge
fluctuations, Coulomb effects were found to persist in all samples including
one with the effective conductance 8 times higher than the quantum value (6.45
k). A good agreement between our experimental data and
theoretical results for the strong tunneling limit is found. A reliable
operation of transistors with conductances 3-4 times larger than the quantum
value is demonstrated.Comment: revtex, 4 page
Strong Electron Tunneling through a Small Metallic Grain
Electron tunneling through mesoscopic metallic grains can be treated
perturbatively only provided the tunnel junction conductances are sufficiently
small. If it is not the case, fluctuations of the grain charge become strong.
As a result (i) contributions of all -- including high energy -- charge states
become important and (ii) excited charge states become broadened and
essentially overlap. At the same time the grain charge remains discrete and the
system conductance -periodically depends on the gate charge. We develop a
nonperturbative approach which accounts for all these features and calculate
the temperature dependent conductance of the system in the strong tunneling
regime at different values of the gate charge.Comment: revtex, 8 pages, 2 .ps figure
Statistics of Current Fluctuations and Electron-Electron Interactions in Mesoscopic Coherent Conductors
We formulate a general path integral approach which describes statistics of
current fluctuations in mesoscopic coherent conductors at arbitrary frequencies
and in the presence of interactions. Applying this approach to the
non-interacting case, we analyze the frequency dispersion of the third cumulant
of the current operator at frequencies well below both the inverse
charge relaxation time and the inverse electron dwell time. This dispersion
turns out to be important in the frequency range comparable to applied
voltages. For comparatively transparent conductors it may lead to the sign
change of . We also analyze the behavior of the second cumulant of
the current operator (current noise) in the presence of
electron-electron interactions. In a wide range of parameters we obtain
explicit universal dependencies of on temperature, voltage and
frequency. We demonstrate that Coulomb interaction decreases the Nyquist noise.
In this case the interaction correction to the noise spectrum is governed by
the combination , where is the transmission of the
-th conducting mode. The effect of electron-electron interactions on the
shot noise is more complicated. At sufficiently large voltages we recover two
different interaction corrections entering with opposite signs. The net result
is proportional to , i.e. Coulomb interaction
decreases the shot noise at low transmissions and increases it at high
transmissions.Comment: 12 pages, 3 figures. To be published in the Proceedings of the SPIE
Symposium on Fluctuations and Noise, Maspalomas, Grand Canaria, Spain (May
2004
Coulomb Interaction and Quantum Transport through a Coherent Scatterer
An interplay between charge discreteness, coherent scattering and Coulomb
interaction yields nontrivial effects in quantum transport. We derive a real
time effective action and an equivalent quantum Langevin equation for an
arbitrary coherent scatterer and evaluate its current-voltage characteristics
in the presence of interactions. Within our model, at large conductances
and low (but outside the instanton-dominated regime) the interaction
correction to saturates and causes conductance suppression by a universal
factor which depends only on the type of the conductor.Comment: 4 pages, no figure
Electron transport and current fluctuations in short coherent conductors
Employing a real time effective action formalism we analyze electron
transport and current fluctuations in comparatively short coherent conductors
in the presence of electron-electron interactions. We demonstrate that, while
Coulomb interaction tends to suppress electron transport, it may {\it strongly
enhance} shot noise in scatterers with highly transparent conducting channels.
This effect of excess noise is governed by the Coulomb gap observed in the
current-voltage characteristics of such scatterers. We also analyze the
frequency dispersion of higher current cumulants and emphasize a direct
relation between electron-electron interaction effects and current fluctuations
in disordered mesoscopic conductors.Comment: 16 pages, 4 figure
Magnetoresistance of n-GaAs at filamentary current flow
A large number of sharp structures are observed in the 4.2 K magnetoresistance of n-GaAs biased above impurity breakdown in a regime where current flow is filamentary. Most of the structures cannot be attributed to spectral properties of the semiconductor such as impact excitation of shallow donors or the magnetoimpurity effect. Experimental results give evidence that these structures are caused by a redistribution of the filamentary current flow when one filament border is swept across an imperfection in the material
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