2,665 research outputs found
Surface Acoustic Wave induced Transport in a Double Quantum Dot
We report on non-adiabatic transport through a double quantum dot under
irradiation of surface acoustic waves generated on-chip. At low excitation
powers, absorption and emission of single and multiple phonons is observed. At
higher power, sequential phonon assisted tunneling processes excite the double
dot in a highly non-equilibrium state. The present system is attractive for
studying electron-phonon interaction with piezoelectric coupling.Comment: 4 pages, 3 figure
Molecular states in a one-electron double quantum dot
The transport spectrum of a strongly tunnel-coupled one-electron double
quantum dot electrostatically defined in a GaAs/AlGaAs heterostructure is
studied. At finite source-drain-voltage we demonstrate the unambiguous
identification of the symmetric ground state and the antisymmetric excited
state of the double well potential by means of differential conductance
measurements. A sizable magnetic field, perpendicular to the two-dimensional
electron gas, reduces the extent of the electronic wave-function and thereby
decreases the tunnel coupling. A perpendicular magnetic field also modulates
the orbital excitation energies in each individual dot. By additionally tuning
the asymmetry of the double well potential we can align the chemical potentials
of an excited state of one of the quantum dots and the ground state of the
other quantum dot. This results in a second anticrossing with a much larger
tunnel splitting than the anticrossing involving the two electronic ground
states.Comment: 4 pages, 4 figures; EP2DS-16 conference contributio
Gas signatures of Herbig Ae/Be disks probed with Herschel SPIRE spectroscopy
Herbig Ae/Be objects, like their lower mass counterparts T Tauri stars, are
seen to form a stable circumstellar disk which is initially gas-rich and could
ultimately form a planetary system. We present Herschel SPIRE 460-1540 GHz
spectra of five targets out of a sample of 13 young disk sources, showing line
detections mainly due to warm CO gas.Comment: to be published in proceedings of IAU symposium 299 (Victoria, BC,
Canada, June 2013
Molecular junctions in the Coulomb blockade regime: rectification and nesting
Quantum transport through single molecules is very sensitive to the strength
of the molecule-electrode contact. Here, we investigate the behavior of a model
molecular junction weakly coupled to external electrodes in the case where
charging effects do play an important role (Coulomb blockade regime). As a
minimal model we consider a molecular junction with two spatially separated
donor and acceptor sites. Depending on their mutual coupling to the electrodes,
the resulting transport observables show well defined features such as
rectification effects in the I-V characteristics and nesting of the stability
diagrams. To be able to accomplish these results, we have developed a theory
which allows to explore the charging regime via the nonequilibrium Green
function formalism parallel to the widely used master equation technique. Our
results, beyond their experimental relevance, offer a transparent framework for
the systematic and modular inclusion of a richer physical phenomenology
Molecular gas and dust influenced by massive protostars:spectral surveys in the far-infrared and submillimeter
Pauli-Spin-Blockade Transport through a Silicon Double Quantum Dot
We present measurements of resonant tunneling through discrete energy levels
of a silicon double quantum dot formed in a thin silicon-on-insulator layer. In
the absence of piezoelectric phonon coupling, spontaneous phonon emission with
deformation-potential coupling accounts for inelastic tunneling through the
ground states of the two dots. Such transport measurements enable us to observe
a Pauli spin blockade due to effective two-electron spin-triplet correlations,
evident in a distinct bias-polarity dependence of resonant tunneling through
the ground states. The blockade is lifted by the excited-state resonance by
virtue of efficient phonon emission between the ground states. Our experiment
demonstrates considerable potential for investigating silicon-based spin
dynamics and spin-based quantum information processing.Comment: 10 pages,3 figure
Negative differential conductance and magnetoresistance oscillations due to spin accumulation in ferromagnetic double-island devices
Spin-dependent electronic transport in magnetic double-island devices is
considered theoretically in the sequential tunneling regime. Electric current
and tunnel magnetoresistance are analyzed as a function of the bias voltage and
spin relaxation time in the islands. It is shown that the interplay of spin
accumulation on the islands and charging effects leads to periodic modification
of the differential conductance and tunnel magnetoresistance. For a
sufficiently long spin relaxation time, the modulations are associated with
periodic oscillations of the sign of both the tunnel magnetoresistance and
differential conductance
Non-Markovian dynamics of double quantum dot charge qubits due to acoustic phonons
We investigate the dynamics of a double quantum dot charge qubit which is
coupled to piezoelectric acoustic phonons, appropriate for GaAs
heterostructures. At low temperatures, the phonon bath induces a non-Markovian
dynamical behavior of the oscillations between the two charge states of the
double quantum dot. Upon applying the numerically exact quasiadiabatic
propagator path-integral scheme, the reduced density matrix of the charge qubit
is calculated, thereby avoiding the Born-Markov approximation. This allows a
systematic study of the dependence of the Q-factor on the lattice temperature,
on the size of the quantum dots, as well as on the interdot coupling. We
calculate the Q-factor for a recently realized experimental setup and find that
it is two orders of magnitudes larger than the measured value, indicating that
the decoherence due to phonons is a subordinate mechanism.Comment: 5 pages, 7 figures, replaced with the version to appear in Phys. Rev.
Transient regime in non-linear transport through many-level quantum dots
We investigate the nonstationary electronic transport in noninteracting
nanostructures driven by a finite bias and time-dependent signals applied at
their contacts to the leads. The systems are modelled by a tight-binding
Hamiltonian and the transient currents are computed from the non-equilibrium
Green-Keldysh formalism. The numerical implementation is not restricted to weak
coupling to the leads and does not imply the wide-band limit assumption for the
spectral width of the leads. As an application of the method we study in detail
the transient behavior and the charge dynamics in single and double quantum
dots connected to leads by a step-like potential, but the method allows as well
the consideration of non-periodic potentials or short pulses. We show that when
the higher energy levels of the isolated system are located within the bias
window of the leads the transient current approaches the steady state in a
non-oscillatory smooth fashion. At moderate coupling to the leads and fixed
bias the transient acquires a step-like structure, the length of the steps
increasing with the system size. The number of levels inside a finite bias
window can be tuned by a constant gate potential. We find also that the
transient behavior depends on the specific way of coupling the leads to the
mesoscopic system.Comment: RevTeX, 12 pages, 11 include .eps figure
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