3,050 research outputs found
DNA double helices for single molecule electronics
The combination of self-assembly and electronic properties as well as its
true nanoscale dimensions make DNA a promising candidate for a building block
of single molecule electronics. We argue that the intrinsic double helix
conformation of the DNA strands provides a possibility to drive the electric
current through the DNA by the perpendicular electric (gating) field. The
transistor effect in the poly(G)-poly(C) synthetic DNA is demonstrated within a
simple model approach. We put forward experimental setups to observe the
predicted effect and discuss possible device applications of DNA. In
particular, we propose a design of the single molecule analog of the Esaki
diode.Comment: 4 pages, 4 figur
Spin-dependent pump current and noise in an adiabatic quantum pump based on domain walls in a magnetic nanowire
We study the pump current and noise properties in an adiabatically modulated
magnetic nanowire with double domain walls (DW). The modulation is brought
about by applying a slowly oscillating magnetic and electric fields with a
controllable phase difference. The pumping mechanism resembles the case of the
quantum dot pump with two-oscillating gates. The pump current, shot noise, and
heat flow show peaks when the Fermi energy matches with the spin-split resonant
levels localized between the DWs. The peak height of the pump current is an
indicator for the lifetime of the spin-split quasistationary states between the
DWs. For sharp DWs, the energy absorption from the oscillating fields results
in side-band formations observable in the pump current. The pump noise carries
information on the correlation properties between the nonequilibrium electrons
and the quasi-holes created by the oscillating scatterer. The ratio between the
pump shot noise and the heat flow serves as an indicator for quasi-particle
correlation.Comment: 18 pages, 5 figure
Noise properties of two single electron transistors coupled by a nanomechanical resonator
We analyze the noise properties of two single electron transistors (SETs)
coupled via a shared voltage gate consisting of a nanomechanical resonator.
Working in the regime where the resonator can be treated as a classical system,
we find that the SETs act on the resonator like two independent heat baths. The
coupling to the resonator generates positive correlations in the currents
flowing through each of the SETs as well as between the two currents. In the
regime where the dynamics of the resonator is dominated by the back-action of
the SETs, these positive correlations can lead to parametrically large
enhancements of the low frequency current noise. These noise properties can be
understood in terms of the effects on the SET currents of fluctuations in the
state of a resonator in thermal equilibrium which persist for times of order
the resonator damping time.Comment: Accepted for publication in Phys. Rev.
Improvement of current-control induced by oxide crenel in very short field-effect-transistor
A 2D quantum ballistic transport model based on the non-equilibrium Green's
function formalism has been used to theoretically investigate the effects
induced by an oxide crenel in a very short (7 nm) thin-film
metal-oxide-semiconductor-field-effect-transistor. Our investigation shows that
a well adjusted crenel permits an improvement of on-off current ratio Ion/Ioff
of about 244% with no detrimental change in the drive current Ion. This
remarkable result is explained by a nontrivial influence of crenel on
conduction band-structure in thin-film. Therefore a well optimized crenel seems
to be a good solution to have a much better control of short channel effects in
transistor where the transport has a strong quantum behavior
Collision duration time for optical phonon emission in semiconductors
The time required to emit an optical (polar and intervalley) phonon by a nearly-free electron in a semiconductor is evaluated using a nonequilibrium Green's-function formalism. The leading idea of the work is that the so-called "collision duration" is related to the time required to build up correlation between the initial and the final state, and then to destroy this correlation as the collision is completed. The use of the nonequilibrium Green's-function formalism gives us the possibility to evaluate explicitly the effects of the correlations in time. Our approach is based on two crucial assumptions: we build the self-energy from only the polarization field of the polar-optical phonon; that is, the self-energy is a function of a single time and position, and we introduce the electron correlation function between the initial and the final states, written in terms of a generalized less-than Green's function in the momentum variables. We derive an analytical expression for the probability for a carrier to end up in a final state k as a consequence of the emission of a phonon as a function of time. We find that the probability rises to the "Fermi golden rule" result within a few femtoseconds. If the total lifetime broadening of the initial state is comparable to the scattering time, the probability oscillates as it approaches the asymptotic value. For larger initial-state broadening (due to more scattering processes), these oscillations disappear
Magnetoconductance of the quantum spin Hall state
We study numerically the edge magnetoconductance of a quantum spin Hall
insulator in the presence of quenched nonmagnetic disorder. For a finite
magnetic field B and disorder strength W on the order of the bulk gap E_g, the
conductance deviates from its quantized value in a manner which appears to be
linear in |B| at small B. The observed behavior is in qualitative agreement
with the cusp-like features observed in recent magnetotransport measurements on
HgTe quantum wells. We propose a dimensional crossover scenario as a function
of W, in which for weak disorder W < E_g the edge liquid is analogous to a
disordered spinless 1D quantum wire, while for strong disorder W > E_g, the
disorder causes frequent virtual transitions to the 2D bulk, where the
originally 1D edge electrons can undergo 2D diffusive motion and 2D
antilocalization.Comment: 5 pages, 3 figure
Low-Energy Conductivity of Single- and Double-Layer Graphene from the Uncertainty Principle
The minimum conductivity value as well as the linear dependence of
conductivity on the charge density near the Dirac point in single and
doublelayer graphene is derived from the energy-time uncertainty principle
applied to ballistic charge carriers
Scattering of Dirac electrons by circular mass barriers: valley filter and resonant scattering
The scattering of two-dimensional (2D) massless Dirac electrons is
investigated in the presence of a random array of circular mass barriers. The
inverse momentum relaxation time and the Hall factor are calculated and used to
obtain parallel and perpendicular resistivity components within linear
transport theory. We found a non zero perpendicular resistivity component which
has opposite sign for electrons in the different K and K' valleys. This
property can be used for valley filter purposes. The total cross-section for
scattering on penetrable barriers exhibit resonances due to the presence of
quasi-bound states in the barriers that show up as sharp gaps in the
cross-section while for Schr\"{o}dinger electrons they appear as peaks.Comment: 10 pages, 11 figure
Anomalous Josephson Current in Junctions with Spin-Polarizing Quantum Point Contacts
We consider a ballistic Josephson junction with a quantum point contact in a
two-dimensional electron gas with Rashba spin-orbit coupling. The point contact
acts as a spin filter when embedded in a circuit with normal electrodes. We
show that with an in-plane external magnetic field an anomalous supercurrent
appears even for zero phase difference between the superconducting electrodes.
In addition, the external field induces large critical current asymmetries
between the two flow directions, leading to supercurrent rectifying effects.Comment: 4 pages, 4 figures, to appear in PR
Quantum teleportation of electrons in quantum wires with surface acoustic waves
We propose and numerically simulate a semiconductor device based on coupled
quantum wires, suitable for deterministic quantum teleportation of electrons
trapped in the minima of surface acoustic waves.We exploit a network of
interacting semiconductor quantum wires able to provide the universal set of
gates for quantum information processing, with the qubit defined by the
localization of a single electron in one of two coupled channels.The numerical
approach is based on a time-dependent solution of the three-particle
Schr\"odinger equation. First, a maximally entangled pair of electrons is
obtained via Coulomb interaction between carriers in different channels. Then,
a complete Bell-state measurement involving one electron from this pair and a
third electron is performed. Finally, the teleported state is reconstructed by
means of local one-qubit operations. The large estimated fidelity explicitely
suggests that an efficient teleportation process could be reached in an
experimental setup.Comment: 7 pages,4 figures, 1 tabl
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