455 research outputs found
Spin Fine Structure in Optically Excited Quantum Dot Molecules
The interaction between spins in coupled quantum dots is revealed in distinct
fine structure patterns in the measured optical spectra of InAs/GaAs double
quantum dot molecules containing zero, one, or two excess holes. The fine
structure is explained well in terms of a uniquely molecular interplay of spin
exchange interactions, Pauli exclusion and orbital tunneling. This knowledge is
critical for converting quantum dot molecule tunneling into a means of
optically coupling not just orbitals, but spins.Comment: 10 pages, 7 figures, added material, (published
Thermopower of a Kondo-correlated quantum dot
The thermopower of a Kondo-correlated gate-defined quantum dot is studied
using a current heating technique. In the presence of spin correlations the
thermopower shows a clear deviation from the semiclassical Mott relation
between thermopower and conductivity. The strong thermopower signal indicates a
significant asymmetry in the spectral density of states of the Kondo resonance
with respect to the Fermi energies of the reservoirs. The observed behavior can
be explained within the framework of an Anderson-impurity model.
Keywords: Thermoelectric and thermomagnetic effects, Coulomb blockade, single
electron tunneling, Kondo-effect
PACS Numbers: 72.20.Pa, 73.23.HkComment: 4 pages, 4 figures, revised version, changed figure
Photoluminescence Spectroscopy of the Molecular Biexciton in Vertically Stacked Quantum Dot Pairs
We present photoluminescence studies of the molecular neutral
biexciton-exciton spectra of individual vertically stacked InAs/GaAs quantum
dot pairs. We tune either the hole or the electron levels of the two dots into
tunneling resonances. The spectra are described well within a few-level,
few-particle molecular model. Their properties can be modified broadly by an
electric field and by structural design, which makes them highly attractive for
controlling nonlinear optical properties.Comment: 4 pages, 5 figures, (v2, revision based on reviewers comments,
published
Sequential and co-tunneling behavior in the temperature-dependent thermopower of few-electron quantum dots
We have studied the temperature dependent thermopower of gate-defined,
lateral quantum dots in the Coulomb blockade regime using an electron heating
technique. The line shape of the thermopower oscillations depends strongly on
the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from
a pure sawtooth- to an intermitted sawtooth-like line shape is observed. The
latter is attributed to the increasing dominance of cotunneling processes in
the Coulomb blockade regime at low temperatures.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Thermoelectric effects in quantum dots
We report a numerical renormalization-group study of the thermoelectric
effect in the single-electron transistor (SET) and side-coupled geometries. As
expected, the computed thermal conductance and thermopower curves show
signatures of the Kondo effect and of Fano interference. The thermopower curves
are also affected by particle-hole asymmetry.Comment: 8 pages with 3 figures; accepted for publication in Physica B
(special issue 'Strongly Correlated Electron Systems-SCES2008'
Measuring Temperature Gradients over Nanometer Length Scales
When a quantum dot is subjected to a thermal gradient, the temperature of
electrons entering the dot can be determined from the dot's thermocurrent if
the conductance spectrum and background temperature are known. We demonstrate
this technique by measuring the temperature difference across a 15 nm quantum
dot embedded in a nanowire. This technique can be used when the dot's energy
states are separated by many kT and will enable future quantitative
investigations of electron-phonon interaction, nonlinear thermoelectric
effects, and the effciency of thermoelectric energy conversion in quantum dots.Comment: 6 pages, 5 figure
Thermal rectification effects of multiple semiconductor quantum dot junctions
Based on the multiple energy level Anderson model, this study theoretically
examines the thermoelectric effects of semiconductor quantum dots (QDs) in the
nonlinear response regime. The charge and heat currents in the sequential
tunneling process are calculated by using the Keldysh Green's function
technique. Results show that the thermal rectification effect can be observed
in a multiple QD junction system, whereas the tunneling rate, size fluctuation,
and location distribution of QD significantly influence the rectification
efficiency.Comment: 5 pages, 8figure
Energy level shift of quantum systems via the electric Aharonov-Bohm effect
A novel version of the electric Aharonov-Bohm effect is proposed where the
quantum system which picks up the Aharonov-Bohm phase is confined to a Faraday
cage with a time varying, spatially uniform scalar potential. The electric and
magnetic fields in this region are effectively zero for the entire period of
the experiment. The observable consequence of this version of the electric
Aharonov-Bohmn effect is to shift the energy levels of the quantum system
rather than shift the fringes of the 2-slit interference pattern. We show a
strong mathematical connection between this version of the scalar electric AB
effect and the AC Stark effect.Comment: 14 pages revtex, 4 figures. Added references and changes made to
address referee comments. To be published in PR
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