142 research outputs found
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron Systems
We measure the effect of externally applied broadband Nyquist noise on the
intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas
at low temperatures. Within the measurement error, the phase coherence time is
unaffected by the externally applied Nyquist noise, including applied noise
temperatures of up to 300 K. The amplitude of the applied Nyquist noise from
100 MHz to 10 GHz is quantitatively determined in the same experiment using a
microwave network analyzer.Comment: 5 pages, 4 figures. Author affiliation clarified; acknowledgements
modified. Replacement reason clarifie
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
Aharonov-Bohm ring with fluctuating flux
We consider a non-interacting system of electrons on a clean one-channel
Aharonov-Bohm ring which is threaded by a fluctuating magnetic flux. The flux
derives from a Caldeira-Leggett bath of harmonic oscillators. We address the
influence of the bath on the following properties: one- and two-particle
Green's functions, dephasing, persistent current and visibility of the
Aharonov-Bohm effect in cotunneling transport through the ring. For the bath
spectra considered here (including Nyquist noise of an external coil), we find
no dephasing in the linear transport regime at zero temperature.
PACS numbers: 73.23.-b, 73.23.Hk, 73.23.Ra, 03.65.YzComment: 17 pages, 8 figures. To be published in PRB. New version contains
minor corrections and additional discussion suggested by referee. A simple
introduction to the basics of dephasing can be found at
http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm
Conductance of the Single Electron Transistor for Arbitrary Tunneling Strength
We study the temperature and gate voltage dependence of the conductance of
the single electron transistor focusing on highly conducting devices. Electron
tunneling is treated nonperturbatively by means of path integral Monte Carlo
techniques and the conductance is determined from the Kubo formula. A
regularized singular value decomposition scheme is employed to calculate the
conductance from imaginary time simulation data. Our findings are shown to
bridge between available analytical results in the semiclassical and
perturbative limits and are found to explain recent experimental results in a
regime not accessible by earlier methods.Comment: 4 pages, 2 figure
Aharonov-Bohm oscillations of a particle coupled to dissipative environments
The amplitude of the Bohm-Aharonov oscillations of a particle moving around a
ring threaded by a magnetic flux and coupled to different dissipative
environments is studied. The decay of the oscillations when increasing the
radius of the ring is shown to depend on the spatial features of the coupling.
When the environment is modelled by the Caldeira-Leggett bath of oscillators,
or the particle is coupled by the Coulomb potential to a dirty electron gas,
interference effects are suppressed beyond a finite length, even at zero
temperature. A finite renormalization of the Aharonov-Bohm oscillations is
found for other models of the environment.Comment: 6 page
Superconductivity in one dimension
Superconducting properties of metallic nanowires can be entirely different
from those of bulk superconductors because of the dominating role played by
thermal and quantum fluctuations of the order parameter. For superconducting
wires with diameters below nm quantum phase slippage is an important
process which can yield a non-vanishing wire resistance down to very low
temperatures. Further decrease of the wire diameter, for typical material
parameters down to nm, results in proliferation of quantum phase
slips causing a sharp crossover from superconducting to normal behavior even at
T=0. A number of interesting phenomena associated both with quantum phase slips
and with the parity effect occur in superconducting nanorings. We review recent
theoretical and experimental activities in the field and demonstrate dramatic
progress in understanding of the phenomenon of superconductivity in
quasi-one-dimensional nanostructures.Comment: 62 pages, 47 figures Misprints corrected, several equations are
adapted to the experimentally relevant diffusive limi
Weak localization, Aharonov–Bohm oscillations and decoherence in arrays of quantum dots
Combining scattering matrix theory with non-linear σ-model and Keldysh technique we develop a unified theoretical approach enabling one to non-perturbatively study the effect of electron–electron interactions on weak localization and Aharonov–Bohm oscillations in arbitrary arrays of quantum dots. Our model embraces weakly disordered conductors, strongly disordered conductors and (iii) metallic quantum dots. In all these cases at T→0 the electron decoherence time is found to saturate to a finite value determined by the universal formula which agrees quantitatively with numerous experimental results. Our analysis provides overwhelming evidence in favor of electron–electron interactions as a universal mechanism for zero temperature electron decoherence in disordered conductors
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