4,058 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
Dynamic Ad-Dimer Twisting Assisted Nanowire Self-Assembly on Si(001)
Based on ab initio total energy calculation, we show that a dynamic ad-dimer twisting assisted (DATA) process plays a crucial role in facilitating a novel structural reconstruction involving surface and subsurface atoms on Si(001). It leads to self-assembly of long nanowires of group-V elements (Bi, Sb) in the trenches of surface dimer vacancy lines (DVLs) with a characteristic double-dimer configuration. The key to this is the lowering of the kinetic barrier by the DATA process in conjunction with a favorable interaction between ad-dimers and step edges in DVLs. The present results provide an excellent account for experimental observations and reveal the atomistic origin and the dynamic transformation path for nanowire self-assembly on Si(001)
A Xenon Condenser with a Remote Liquid Storage Vessel
We describe the design and operation of a system for xenon liquefaction in
which the condenser is separated from the liquid storage vessel. The condenser
is cooled by a pulse tube cryocooler, while the vessel is cooled only by the
liquid xenon itself. This arrangement facilitates liquid particle detector
research by allowing easy access to the upper and lower flanges of the vessel.
We find that an external xenon gas pump is useful for increasing the rate at
which cooling power is delivered to the vessel, and we present measurements of
the power and efficiency of the apparatus.Comment: 22 pages, 7 figures Corrected typos in authors lis
Parametric pumping at finite frequency
We report on a first principles theory for analyzing the parametric electron
pump at a finite frequency. The pump is controlled by two pumping parameters
with phase difference . In the zero frequency limit, our theory predicts
the well known result that the pumped current is proportional to .
For the more general situation of a finite frequency, our theory predicts a
non-vanishing pumped current even when the two driving forces are in phase, in
agreement with the recent experimental results. We present the physical
mechanism behind the nonzero pumped current at , which we found to be
due to photon-assisted processes
Topology of the ground state of two interacting Bose-Einstein condensates
We investigate the spatial patterns of the ground state of two interacting
Bose-Einstein condensates. We consider the general case of two different atomic
species (with different mass and in different hyperfine states) trapped in a
magnetic potential whose eigenaxes can be tilted with respect to the vertical
direction, giving rise to a non trivial gravitational sag. Despite the
complicated geometry, we show that within the Thomas-Fermi approximations and
upon appropriate coordinate transformations, the equations for the density
distributions can be put in a very simple form. Starting from this expressions
we give explicit rules to classify the different spatial topologies which can
be produced, and we discuss how the behavior of the system is influenced by the
inter-atomic scattering length. We also compare explicit examples with the full
numeric Gross-Pitaevskii calculation.Comment: RevTex4, 8 pages, 7 figure
Optimal quantum pump in the presence of a superconducting lead
We investigate the parametric pumping of a hybrid structure consisting of a
normal quantum dot, a normal lead and a superconducting lead. Using the time
dependent scattering matrix theory, we have derived a general expression for
the pumped electric current and heat current. We have also derived the
relationship among the instantaneous pumped heat current, electric current, and
shot noise. This gives a lower bound for the pumped heat current in the hybrid
system similar to that of the normal case obtained by Avron et al
Quantization of adiabatic pumped charge in the presence of superconducting lead
We investigate the parametric electron pumping of a double barrier structure
in the presence of a superconducting lead. The parametric pumping is
facilitated by cyclic variation of the barrier heights and of the
barriers. In the weak coupling regime, there exists a resonance line in the
parameter space so that the energy of the quasi-bound state is in
line with the incoming Fermi energy. Levinson et al found recently that the
pumped charge for each pumping cycle is quantized with for normal
structure when the pumping contour encircles the resonance line. In the
presence of a superconducting lead, we find that the pumped charge is quantized
with the value
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal
nonlinear response function, we derive a nonliear equation in which the mixed
state Hall resistivity can be expressed as an analytical function of magnetic
field, temperature and applied current. This equation enables one to compare
quantitatively the experimental data with theoretical model. We also find some
new scaling relations of the temperature and field dependency of Hall
resistivity. The comparison between our theoretical curves and experimental
data shows a fair agreement.Comment: 4 pages, 3 figure
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