158 research outputs found

### On the scaling approach to electron-electron interactions in a chaotic quantum dot

A scaling theory is used to study the low energy physics of electron-electron
interactions in a double quantum dot. We show that the fact that electrons are
delocalized over two quantum dots does not affect the instability criterion for
the description of electron-electron interactions in terms of a ``universal
interaction Hamiltonian''.Comment: 4 pages, 3 figure

### Interaction-induced dephasing of Aharonov-Bohm oscillations

We study the effect of the electron-electron interaction on the amplitude of
mesoscopic Aharonov-Bohm oscillations in quasi-one-dimensional (Q1D) diffusive
rings. We show that the dephasing length L_phi^AB governing the damping factor
exp(-2piR / L_phi^AB) of the oscillations is parametrically different from the
common dephasing length for the Q1D geometry. This is due to the fact that the
dephasing is governed by energy transfers determined by the ring circumference
2piR, making L_phi^AB R-dependent.Comment: 4 pages, 2 figures. Minor changes, final version published in PR

### Interaction corrections to the Hall coefficient at intermediate temperatures

We investigate the effect of electron-electron interaction on the temperature
dependence of the Hall coefficient of 2D electron gas at arbitrary relation
between the temperature $T$ and the elastic mean-free time $\tau$. At small
temperature $T\tau \ll \hbar$ we reproduce the known relation between the
logarithmic temperature dependences of the Hall coefficient and of the
longitudinal conductivity. At higher temperatures, this relation is violated
quite rapidly; correction to the Hall coefficient becomes $\propto 1/T$ whereas
the longitudinal conductivity becomes linear in temperature.Comment: 4 pages, 3 .eps figure

### Mesoscopic Aharonov-Bohm oscillations in metallic rings

We study the amplitude of mesoscopic Aharonov-Bohm oscillations in
quasi-one-dimensional (Q1D) diffusive rings. We consider first the
low-temperature limit of a fully coherent sample. The variance of oscillation
harmonics is calculated as a function of the length of the leads attaching the
ring to reservoirs. We further analyze the regime of relatively high
temperatures, when the dephasing due to electron-electron interaction
suppresses substantially the oscillations. We show that the dephasing length
L_phi^AB governing the damping factor exp(-2pi R /L_phi^AB) of the oscillations
is parametrically different from the common dephasing length for the Q1D
geometry. This is due to the fact that the dephasing is governed by energy
transfers determined by the ring circumference 2pi R, making L_phi^AB
R-dependent.Comment: 16 pages, 4 figures, to appear in proceedings of NATO/Euresco
Conference "Fundamental Problems of Mesoscopic Physics: Interactions and
Decoherence", Granada (Spain), September 200

### Interaction corrections at intermediate temperatures: dephasing time

We calculate the temperature dependence of the weak localization correction
in a two dimensional system at arbitrary relation between temperature, $T$ and
the elastic mean free time. We describe the crossover in the dephasing time
${\tau_\phi(T)}$ between the high temperature, $1/\tau_\phi \simeq T^2 \ln T$,
and the low temperature $1/\tau_\phi \simeq T$ behaviors. The prefactors in
these dependences are not universal, but are determined by the Fermi liquid
constant characterising the spin exchange interaction.Comment: 4 pages, to appear in PRB, minor errors corrected, added reference

### Dephasing of Electrons in Mesoscopic Metal Wires

We have extracted the phase coherence time $\tau_{\phi}$ of electronic
quasiparticles from the low field magnetoresistance of weakly disordered wires
made of silver, copper and gold. In samples fabricated using our purest silver
and gold sources, $\tau_{\phi}$ increases as $T^{-2/3}$ when the temperature
$T$ is reduced, as predicted by the theory of electron-electron interactions in
diffusive wires. In contrast, samples made of a silver source material of
lesser purity or of copper exhibit an apparent saturation of $\tau_{\phi}$
starting between 0.1 and 1 K down to our base temperature of 40 mK. By
implanting manganese impurities in silver wires, we show that even a minute
concentration of magnetic impurities having a small Kondo temperature can lead
to a quasi saturation of $\tau_{\phi}$ over a broad temperature range, while
the resistance increase expected from the Kondo effect remains hidden by a
large background. We also measured the conductance of Aharonov-Bohm rings
fabricated using a very pure copper source and found that the amplitude of the
$h/e$ conductance oscillations increases strongly with magnetic field. This set
of experiments suggests that the frequently observed ``saturation'' of
$\tau_{\phi}$ in weakly disordered metallic thin films can be attributed to
spin-flip scattering from extremely dilute magnetic impurities, at a level
undetectable by other means.Comment: 16 pages, 11 figures, to be published in Physical Review

### Is weak temperature dependence of electron dephasing possible?

The first-principle theory of electron dephasing by disorder-induced two
state fluctuators is developed. There exist two mechanisms of dephasing. First,
dephasing occurs due to direct transitions between the defect levels caused by
inelastic electron-defect scattering. The second mechanism is due to violation
of the time reversal symmetry caused by time-dependent fluctuations of the
scattering potential. These fluctuations originate from an interaction between
the dynamic defects and conduction electrons forming a thermal bath. The first
contribution to the dephasing rate saturates as temperature decreases. The
second contribution does not saturate, although its temperature dependence is
rather weak, $\propto T^{1/3}$. The quantitative estimates based on the
experimental data show that these mechanisms considered can explain the weak
temperature dependence of the dephasing rate in some temperature interval.
However, below some temperature dependent on the model of dynamic defects the
dephasing rate tends rapidly to zero. The relation to earlier studies of the
dephasing caused by the dynamical defects is discussed.Comment: 14 pages, 6 figures, submitted to PR

### Quantum-Limited Measurement and Information in Mesoscopic Detectors

We formulate general conditions necessary for a linear-response detector to
reach the quantum limit of measurement efficiency, where the
measurement-induced dephasing rate takes on its minimum possible value. These
conditions are applicable to both non-interacting and interacting systems. We
assess the status of these requirements in an arbitrary non-interacting
scattering based detector, identifying the symmetries of the scattering matrix
needed to reach the quantum limit. We show that these conditions are necessary
to prevent the existence of information in the detector which is not extracted
in the measurement process.Comment: 13 pages, 1 figur

### Dephasing at Low Temperatures

We discuss the significance and the calculation of dephasing at low
temperatures. The particle is moving diffusively due to a static disorder
configuration, while the interference between classical paths is suppressed due
to the interaction with a dynamical environment. At high temperatures we may
use the `white noise approximation' (WNA), while at low temperatures we
distinguish the contribution of `zero point fluctuations' (ZPF) from the
`thermal noise contribution' (TNC). We study the limitations of the above
semiclassical approach and suggest the required modifications. In particular we
find that the ZPF contribution becomes irrelevant for thermal motion.Comment: 4 pages, 1 figure, clearer presentatio

### Quantum Pumping in the Magnetic Field: Role of Discrete Symmetries

We consider an effect of the discrete spatial symmetries and magnetic field
on the adiabatic charge pumping in mesoscopic systems. In general case, there
is no symmetry of the pumped charge with respect to the inversion of magnetic
field Q(B) \neq Q(-B). We find that the reflection symmetries give rise to
relations Q(B)=Q(-B) or Q(B)=-Q(-B) depending on the orientation of the
reflection axis. In presence of the center of inversion, Q(B) = 0. Additional
symmetries may arise in the case of bilinear pumping.Comment: 4 page

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