9,520 research outputs found

### Evidence for magnetoplasmon character of the cyclotron resonance response of a two-dimensional electron gas

Experimental results on the absolute magneto-transmission of a series of high
density, high mobility GaAs quantum wells are compared with the predictions of
a recent magnetoplasmon theory for values of the filling factor above 2. We
show that the magnetoplasmon picture can explain the non-linear features
observed in the magnetic field evolution of the cyclotron resonance energies
and of the absorption oscillator strength. This provides experimental evidence
that inter Landau level excitations probed by infrared spectroscopy need to be
considered as many body excitations in terms of magnetoplasmons: this is
especially true when interpreting the oscillator strengths of the cyclotron
transitions

### 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 $e$-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

### 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$\Omega$)$^{-1}$. 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

### 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 $G_0$
and low $T$ (but outside the instanton-dominated regime) the interaction
correction to $G_0$ saturates and causes conductance suppression by a universal
factor which depends only on the type of the conductor.Comment: 4 pages, no 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

### 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

### Persistent current noise and electron-electron interactions

We analyze fluctuations of persistent current (PC) produced by a charged
quantum particle moving in a ring and interacting with a dissipative
environment formed by diffusive electron gas. We demonstrate that in the
presence of interactions such PC fluctuations persist down to zero temperature.
In the case of weak interactions and/or sufficiently small values of the ring
radius $R$ PC noise remains coherent and can be tuned by external magnetic flux
$\Phi_x$ piercing the ring. In the opposite limit of strong interactions and/or
large values of $R$ fluctuations in the electronic bath strongly suppress
quantum coherence of the particle down to $T=0$ and induce incoherent
$\Phi_x$-independent current noise in the ring which persists even at
$\Phi_x=0$ when the average PC is absent.Comment: 12 pages, 8 figure

### Charge Fluctuations in the Single Electron Box

Quantum fluctuations of the charge in the single electron box are
investigated. Based on a diagrammatic expansion we calculate the average island
charge number and the effective charging energy in third order in the tunneling
conductance. Near the degeneracy point where the energy of two charge states
coincides, the perturbative approach fails, and we explicitly resum the leading
logarithmic divergencies to all orders. The predictions for zero temperature
are compared with Monte Carlo data and with recent renormalization group
results. While good agreement between the third order result and numerical data
justifies the perturbative approach in most of the parameter regime relevant
experimentally, near the degeneracy point and at zero temperature the
resummation is shown to be insufficient to describe strong tunneling effects
quantitatively. We also determine the charge noise spectrum employing a
projection operator technique. Former perturbative and semiclassical results
are extended by the approach.Comment: 20 pages, 15 figure

### Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions

Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e.
junctions with resistances comparable to, or less than, the quantum resistance
$R_{\rm q}\equiv h/e^2\approx 25.8$ k$\Omega$) have been studied experimentally
and theoretically. Our experimental data demonstrate that -- in agreement with
previous results on single- and double-junction systems -- Coulomb blockade
effects survive even in the strong tunneling regime and are still clearly
visible for junction resistances as low as 1 k$\Omega$. We have developed a
quasiclassical theory of electron transport in junction arrays in the strong
tunneling regime. Good agreement between the predictions of this theory and the
experimental data has been observed. We also show that, due to both heating
effects and a relatively large correction to the linear relation between the
half-width of the conductance dip around zero bias voltage, $V_{1/2}$, and the
measured electronic temperature, such arrays are inferior to those
conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the
desired correction to the half-width, $\Delta V_{1/2}$, can be determined
rather easily and it is proportional to the magnitude of the conductance dip
around zero bias voltage, $\Delta G$. The constant of proportionality is a
function of the ratio of the junction and quantum resistances, $R/R_{\rm q}$,
and it is a pure strong tunneling effect.Comment: LaTeX file + five postscript figure

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