273 research outputs found
Nonequilibrium Green function modelling of transport in mesoscopic systems
A generalized Landauer formula, derived with the methods due to Keldysh, and
Baym and Kadanoff, is gaining widespread use in the modeling of transport in a
large number of different mesoscopic systems. We review some of the recent
developments, including transport in semiconductor superlattices, calculation
of noise, and nanoelectromechanical systems.Comment: Contribution to "Progress in Nonequilibrium Green Functions",
Dresden, Germany, 19-22 August, Editor: Michael Bonit
Signatures of adatom effects in the quasiparticle spectrum of Li-doped graphene
We study the spectral function and quasiparticle scattering in Li-decorated
graphene (Li@graphene) with an atomistic -matrix formalism and uncover
adatom-induced spectral effects which shed light on experimentally observed
angle-resolved photoemission spectroscopy (ARPES) features. From transport
studies, alkali adatoms are known to introduce charged-impurity scattering
limiting the carrier mobility. Here, we demonstrate that Li adatoms furthermore
give rise to a low-energy impurity band centered at the point which
originates from the hybridization between the atomic 2s state of the Li adatoms
and graphene "surface" states. We show that the impurity band is strongly
dependent on the concentration of Li adatoms, and aligns with
the Li-induced Fermi level on the Dirac cone at
(). Finally, we show that adatom-induced
quasiparticle scattering increases dramatically at energies above close to the van Hove singularity in the graphene density of
states (DOS), giving rise to a large linewidth broadening on the Dirac cone
with a concomitant downshift and a characteristic kink in the conduction band.
Our findings are highly relevant for future studies of ARPES, transport, and
superconductivity in adatom-doped graphene.Comment: 6 pages, 4 figures, and supplemental material. Published versio
Mesoscopic photon heat transistor
We show that the heat transport between two bodies, mediated by
electromagnetic fluctuations, can be controlled with an intermediate quantum
circuit - leading to the device concept Mesoscopic Photon Heat Transistor
(MPHT). Our theoretical analysis is based on a novel Meir-Wingreen-Landauer
type of conductance formula, which gives the photonic heat current through an
arbitrary circuit element coupled to two dissipative reservoirs at finite
temperatures. As an illustration we present an exact solution for the case when
the intermediate circuit can be described as an electromagnetic resonator. We
discuss in detail how the MPHT can be implemented experimentally in terms of a
flux-controlled SQUID circuit.Comment: 4 pages, 3 figure
Correlated Coulomb drag in capacitively coupled quantum-dot structures
We study theoretically Coulomb drag in capacitively coupled quantum dots
(CQDs) -- a biasdriven dot coupled to an unbiased dot where transport is due to
Coulomb mediated energy transfer drag. To this end, we introduce a
master-equation approach which accounts for higher-order tunneling
(cotunneling) processes as well as energy-dependent lead couplings, and
identify a mesoscopic Coulomb drag mechanism driven by nonlocal multi-electron
cotunneling processes. Our theory establishes the conditions for a nonzero drag
as well as the direction of the drag current in terms of microscopic system
parameters. Interestingly, the direction of the drag current is not determined
by the drive current, but by an interplay between the energy-dependent lead
couplings. Studying the drag mechanism in a graphene-based CQD heterostructure,
we show that the predictions of our theory are consistent with recent
experiments on Coulomb drag in CQD systems.Comment: 6 pages, 4 figures + supplementary. Published versio
Quantum transport: The link between standard approaches in superlattices
Theories describing electrical transport in semiconductor superlattices can
essentially be divided in three disjoint categories: i) transport in a
miniband; ii) hopping between Wannier-Stark ladders; and iii) sequential
tunneling. We present a quantum transport model, based on nonequilibrium Green
functions, which, in the appropriate limits, reproduces the three conventional
theories, and describes the transport in the previously unaccessible region of
the parameter space.Comment: 4 Page
Current responsivity of semiconductor superlattice THz-photon detectors
The current responsivity of a semiconductor superlattice THz-photon detector
is calculated using an equivalent circuit model which takes into account the
finite matching efficiency between a detector antenna and the superlattice in
the presence of parasitic losses. Calculations performed for currently
available superlattice diodes show that both the magnitudes and the roll-off
frequencies of the responsivity are strongly influenced by an excitation of
hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system
in the THz- frequency band. The expected room temperature values of the
responsivity (2-3 A/W in the 1-3 THz-frequency band) range up to several
percents of the quantum efficiency of an ideal superconductor
tunnel junction detector. Properly designed semiconductor superlattice
detectors may thus demonstrate better room temperature THz-photon responsivity
than conventional Schottky junction devices.Comment: Revtex file, uses epsf, 11 pages. 11 eps-figures; EPS-files generated
by scanner, original higher resolution line drawings available from
[email protected] by regular mail or fa
Strain-engineered Majorana Zero Energy Modes and {\phi}0 Josephson State in Black Phosphorus
We develop a theory for strain control of Majorana zero energy modes and
Josephson effect in black phosphorus (BP) devices proximity coupled to a
superconductor. Employing realistic values for the band parameters subject to
strain, we show that the strain closes the intrinsic band gap of BP, however
the proximity effect from the superconductor reopens it and creates Dirac and
Weyl nodes. Our results illustrate that Majorana zero energy flat bands connect
the nodes within the band-inverted regime in which their associated density of
states is localized at the edges of the device. In a ferromagnetically mediated
Josephson configuration, the exchange field induces super-harmonics into the
supercurrent phase relation in addition to a {\phi}0 phase shift, corresponding
to a spontaneous supercurrent, and strain offers an efficient tool to control
these phenomena. We analyze the experimental implications of our findings, and
show that they can pave the way for creating a rich platform for studying
two-dimensional Dirac and Weyl superconductivity
Thermal rectification in nonlinear quantum circuits
We present a theoretical study of radiative heat transport in nonlinear
solid-state quantum circuits. We give a detailed account of heat rectification
effects, i.e. the asymmetry of heat current with respect to a reversal of the
thermal gradient, in a system consisting of two reservoirs at finite
temperatures coupled through a nonlinear resonator. We suggest an
experimentally feasible superconducting circuit employing the Josephson
nonlinearity to realize a controllable low temperature heat rectifier with a
maximal asymmetry of the order of 10%. We also discover a parameter regime
where the rectification changes sign as a function of temperature.Comment: 5 pages, 5 figures; v2: added discussion on rectification sig
Quantum Shuttle in Phase Space
We present a quantum theory of the shuttle instability in electronic
transport through a nanostructure with a mechanical degree of freedom. A phase
space formulation in terms of the Wigner function allows us to identify a
cross-over from the tunnelling to the shuttling regime, thus extending the
previously found classical results to the quantum domain. Further, a new
dynamical regime is discovered, where the shuttling is driven exclusively by
the quantum noise.Comment: 4 pages, 2 figures; minor changes; final version published in Phys.
Rev. Let
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