18,633 research outputs found
A Green-function approach to transport phenomena in quantum pumps
We present a general treatment to study transport phenomena in systems
described by tight-binding Hamiltonians coupled to reservoirs and with one or
more time-periodic potentials. We apply this treatment to the study of
transport phenomena in a double barrier structure with one and two harmonic
potentials. Among other properties, we discuss the origin of the sign of the
net current.Comment: To appear in PR
Current-voltage (I-V) characteristics of armchair graphene nanoribbons under uniaxial strain
The current-voltage (I-V) characteristics of armchair graphene nanoribbons
under a local uniaxial tension are investigated by using first principles
quantum transport calculations. It is shown that for a given value of
bias-voltage, the resulting current depends strongly on the applied tension.
The observed trends are explained by means of changes in the band gaps of the
nanoribbons due to the applied uniaxial tension. In the course of plastic
deformation, the irreversible structural changes and derivation of carbon
monatomic chains from graphene pieces can be monitored by two-probe transport
measurements.Comment: please see the published version at
http://prb.aps.org/abstract/PRB/v81/i20/e20543
Strongly modulated transmissions in gapped armchair graphene nanoribbons with sidearm or on-site gate voltage
We propose two schemes of field-effect transistor based on gapped armchair
graphene nanoribbons connected to metal leads, by introducing sidearms or
on-site gate voltages. We make use of the band gap to reach excellent
switch-off character. By introducing one sidearm or on-site gate to the
graphene nanoribbon, conduction peaks appear inside the gap regime. By further
applying two sidearms or on-site gates, these peaks are broadened to conduction
plateaus with a wide energy window, thanks to the resonance from the dual
structure. The position of the conduction windows inside the gap can be fully
controlled by the length of the sidearms or the on-site gate voltages, which
allows "on" and "off" operations for a specific energy window inside the gap
regime. The high robustness of both the switch-off character and the conduction
windows is demonstrated and shows the feasibility of the proposed dual
structures for real applications.Comment: 6 pages, 6 figure
Graphene membrane as a pressure gauge
Straining graphene results in the appearance of a pseudo-magnetic field which
alters its local electronic properties. Applying a pressure difference between
the two sides of the membrane causes it to bend/bulge resulting in a resistance
change. We find that the resistance changes linearly with pressure for bubbles
of small radius while the response becomes non-linear for bubbles that stretch
almost to the edges of the sample. This is explained as due to the strong
interference of propagating electronic modes inside the bubble. Our
calculations show that high gauge factors can be obtained in this way which
makes graphene a good candidate for pressure sensing.Comment: 5 pages, 4 figure
Broadening of Spectral Lines due to Dynamic Multiple Scattering and the Tully-Fisher Relation
The frequency shift of spectral lines is most often explained by the Doppler
Effect in terms of relative motion, whereas the Doppler broadening of a
particular line mainly depends on the absolute temperature. The Wolf effect on
the other hand deals with the correlation induced spectral change and explains
both the broadening and shift of the spectral lines. In this framework a
relation between the width of the spectral line is related to the redshift z
for the line and hence with the distance. For smaller values of z a relation
similar to the Tully-Fisher relation can be obtained and for larger values of z
a more general relation can be constructed. The derivation of this kind of
relation based on dynamic multiple scattering theory may play a significant
role in explaining the overall spectra of quasi stellar objects. We emphasize
that this mechanism is not applicable for nearby galaxies, .Comment: 18 pages, 5 figures, revised Version has been submitted to Physical
Review A. (2nd author's affiliation corrected
First-Principles Study of Integer Quantum Hall Transitions in Mesoscopic Samples
We perform first principles numerical simulations to investigate resistance
fluctuations in mesoscopic samples, near the transition between consecutive
Quantum Hall plateaus. We use six-terminal geometry and sample sizes similar to
those of real devices. The Hall and longitudinal resistances extracted from the
generalized Landauer formula reproduce all the experimental features uncovered
recently. We then use a simple generalization of the Landauer-B\"uttiker model,
based on the interplay between tunneling and chiral currents -- the co-existing
mechanisms for transport -- to explain the three distinct types of fluctuations
observed, and identify the central region as the critical region.Comment: changes to acknowledgements onl
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