3,837 research outputs found
Electrical pump-and-probe study of spin singlet-triplet relaxation in a quantum dot
Spin relaxation from a triplet excited state to a singlet ground state in a
semiconductor quantum dot is studied by employing an electrical pump-and-probe
method. Spin relaxation occurs via cotunneling when the tunneling rate is
relatively large, confirmed by a characteristic square dependence of the
relaxation rate on the tunneling rate. When cotunneling is suppressed by
reducing the tunneling rate, the intrinsic spin relaxation is dominated by
spin-orbit interaction. We discuss a selection rule of the spin-orbit
interaction based on the observed double-exponential decay of the triplet
state.Comment: 4 pages, 4 figure
Fano-Kondo interplay in a side-coupled double quantum dot
We investigate low-temperature transport characteristics of a side-coupled
double quantum dot where only one of the dots is directly connected to the
leads. We observe Fano resonances, which arise from interference between
discrete levels in one dot and the Kondo effect, or cotunneling in general, in
the other dot, playing the role of a continuum. The Kondo resonance is
partially suppressed by destructive Fano interference, reflecting novel
Fano-Kondo competition. We also present a theoretical calculation based on the
tight-binding model with slave boson mean field approximation, which
qualitatively reproduces the experimental findings.Comment: 4 pages, 4 figure
A rapid and scalable method for multilocus species delimitation using Bayesian model comparison and rooted triplets
Multilocus sequence data provide far greater power to resolve species limits than the single locus data typically used for broad surveys of clades. However, current statistical methods based on a multispecies coalescent framework are computationally demanding, because of the number of possible delimitations that must be compared and time-consuming likelihood calculations. New methods are therefore needed to open up the power of multilocus approaches to larger systematic surveys. Here, we present a rapid and scalable method that introduces two new innovations. First, the method reduces the complexity of likelihood calculations by decomposing the tree into rooted triplets. The distribution of topologies for a triplet across multiple loci has a uniform trinomial distribution when the 3 individuals belong to the same species, but a skewed distribution if they belong to separate species with a form that is specified by the multispecies coalescent. A Bayesian model comparison framework was developed and the best delimitation found by comparing the product of posterior probabilities of all triplets. The second innovation is a new dynamic programming algorithm for finding the optimum delimitation from all those compatible with a guide tree by successively analyzing subtrees defined by each node. This algorithm removes the need for heuristic searches used by current methods, and guarantees that the best solution is found and potentially could be used in other systematic applications. We assessed the performance of the method with simulated, published and newly generated data. Analyses of simulated data demonstrate that the combined method has favourable statistical properties and scalability with increasing sample sizes. Analyses of empirical data from both eukaryotes and prokaryotes demonstrate its potential for delimiting species in real cases
Time-resolved charge fractionalization in inhomogeneous Luttinger liquids
The recent observation of charge fractionalization in single
Tomanga-Luttinger liquids (TLLs) [Kamata et al., Nature Nanotech., 9 177
(2014)] opens new routes for a systematic investigation of this exotic quantum
phenomenon. In this Letter we perform measurements on two adjacent TLLs and put
forward an accurate theoretical framework to address the experiments. The
theory is based on the plasmon scattering approach and can deal with injected
charge pulses of arbitrary shape in TLL regions. We accurately reproduce and
interpret the time-resolved multiple fractionalization events in both single
and double TLLs. The effect of inter-correlations between the two TLLs is also
discussed.Comment: 5 pages + Supplementary Material. To appear in Phys. Rev. B: Rapid.
Com
Non-equilibrium transport through a vertical quantum dot in the absence of spin-flip energy relaxation
We investigate non-equilibrium transport in the absence of spin-flip energy
relaxation in a few-electron quantum dot artificial atom. Novel non-equilibrium
tunneling processes involving high-spin states which cannot be excited from the
ground state because of spin-blockade, and other processes involving more than
two charge states are observed. These processes cannot be explained by orthodox
Coulomb blockade theory. The absence of effective spin relaxation induces
considerable fluctuation of the spin, charge, and total energy of the quantum
dot. Although these features are revealed clearly by pulse excitation
measurements, they are also observed in conventional dc current characteristics
of quantum dots.Comment: accepted for publication in Phys. Rev.Let
Electron counting of single-electron tunneling current
Single-electron tunneling through a quantum dot is detected by means of a radio-frequency single-electron transistor.. Poisson statistics of single-electron-tunneling events are observed from frequency domain measurements, and individual tunneling events are detected in the time-domain measurements. Counting tunneling events gives an accurate current measurement in the saturated current regime, where electrons tunnel into the dot only from one electrode and tunnel out of the dot only to the other electrode. (C) 2004 American Institute of Physics.X119698sciescopu
Exploration of the memory effect on the photon-assisted tunneling via a single quantum dot: A generalized Floquet theoretical approach
The generalized Floquet approach is developed to study memory effect on
electron transport phenomena through a periodically driven single quantum dot
in an electrode-multi-level dot-electrode nanoscale quantum device. The memory
effect is treated using a multi-function Lorentzian spectral density (LSD)
model that mimics the spectral density of each electrode in terms of multiple
Lorentzian functions. For the symmetric single-function LSD model involving a
single-level dot, the underlying single-particle propagator is shown to be
related to a 2 x 2 effective time-dependent Hamiltonian that includes both the
periodic external field and the electrode memory effect. By invoking the
generalized Van Vleck (GVV) nearly degenerate perturbation theory, an
analytical Tien-Gordon-like expression is derived for arbitrary order multi-
photon resonance d.c. tunneling current. Numerically converged simulations and
the GVV analytical results are in good agreement, revealing the origin of
multi- photon coherent destruction of tunneling and accounting for the
suppression of the staircase jumps of d.c. current due to the memory effect.
Specially, a novel blockade phenomenon is observed, showing distinctive
oscillations in the field-induced current in the large bias voltage limit
Intrinsic gap and exciton condensation in the nu_T=1 bilayer system
We investigate the quasiparticle excitation of the bilayer quantum Hall (QH)
system at total filling factor in the limit of
negligible interlayer tunneling under tilted magnetic field. We show that the
intrinsic quasiparticle excitation is of purely pseudospin origin and solely
governed by the inter- and intra-layer electron interactions. A model based on
exciton formation successfully explains the quantitative behavior of the
quasiparticle excitation gap, demonstrating the existence of a link between the
excitonic QH state and the composite fermion liquid. Our results provide a new
insight into the nature of the phase transition between the two states.Comment: 4 pages, 3 figure
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