1,363 research outputs found
Coulomb effects in artificial molecules
We study the capacitance spectra of artificial molecules consisting of two
and three coupled quantum dots from an extended Hubbard Hamiltonian model that
takes into account quantum confinement, intra- and inter-dot Coulomb
interaction and tunneling coupling between all single particle states in
nearest neighbor dots. We find that, for weak coupling, the interdot Coulomb
interaction dominates the formation of a collective molecular state. We also
calculate the effects of correlations on the tunneling probability through the
evaluation of the spectral weights, and corroborate the importance of selection
rules for understanding experimental conductance spectra.Comment: dvi file and 4 postscript figures, all included in uu file. To appear
in Superlatt. and Microstr. Also available at
http://www.phy.ohiou.edu/~ulloa/ulloa.htm
Spin-orbit signatures in the dynamics of singlet-triplet qubits in double quantum dots
We characterize numerically and analytically the signatures of the spin-orbit
interaction in a two-electron GaAs double quantum dot in the presence of an
external magnetic field. In particular, we obtain the return probability of the
singlet state by simulating Landau-Zener voltage detuning sweeps which traverse
the singlet-triplet () resonance. Our results indicate that
non-spin-conserving interdot tunneling processes arising from the spin-orbit
interaction have well defined signatures. These allow direct access to the
spin-orbit interaction scales and are characterized by a frequency shift and
Fourier amplitude modulation of the Rabi flopping dynamics of the
singlet-triplet qubits and . By applying the Bloch-Feshbach
projection formalism, we demonstrate analytically that the aforementioned
effects originate from the interplay between spin-orbit interaction and
processes driven by the hyperfine interaction between the electron spins and
those of the GaAs nuclei
Bipolar spin filter in a quantum dot molecule
We show that the tunable hybridization between two lateral quantum dots
connected to non-magnetic current leads in a `hanging-dot' configuration that
can be used to implement a bipolar spin filter. The competition between Zeeman,
exchange interaction, and interdot tunneling (molecular hybridization) yields a
singlet-triplet transition of the double dot {\it ground state} that allows
spin filtering in Coulomb blockade experiments. Its generic nature should make
it broadly useful as a robust bidirectional spin polarizer.Comment: 5 pages, 3 figures (to appear in Appl. Phys. Lett.
Tunnel spectroscopy in ac-driven quantum dot nanoresonators
Electronic transport in a triple quantum dot shuttle device in the presence
of an ac field is analyzed within a fully quantum mechanical framework. A
generalized density matrix formalism is used to describe the time evolution for
electronic state occupations in a dissipative phonon bath. In the presence of
an ac gate voltage, the electronic states are dressed by photons and the
interplay between photon and vibrational sidebands produces current
characteristics that obey selection rules. Varying the ac parameters allows to
tune the tunneling current features. In particular, we show that coherent
destruction of tunneling can be achieved in our device
Los chongos de Roa Bastos: literatura e identidade Paraguaia em textos contemporâneos
Anais do VI Encontro de Iniciação CientÃfica e II Encontro Anual de Iniciação ao Desenvolvimento Tecnológico e Inovação – EICTI 2017 - 04 a 06 de outubro de 2017 - temática LinguÃstica, Letras e ArtesO surgimento de novos escritores e produções literárias no Paraguai tem
possibilitado maior visibilidade e debate sobre a literatura paraguaia frente a morte de
Augusto Roa Bastos, um dos autores mais reconhecidos do paÃs. Em Los Chongos de
Roa Bastos, antologia de contos de escritores contemporâneos, essa faceta da realidade
literária no paÃs é evidenciada tanto pela ironia na escolha do tÃtulo – por sua referência
ao grande escritor nacional –, quanto pela condição de escritores menores em que esses
novos autores se encontram: com público leitor limitado, com carências editoriais e
vivendo à s sombras de seu cânoneUniversidade Federal da Integração Latino-Americana (Unila); Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq); Fundação Araucária; Parque Tecnológico Itaipu (PTI) e Companhia de Saneamento do Paraná (SANEPAR
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The ENSO signature in sea-surface temperature in the Gulf of California
We analyzed 21 years of sea-surface temperature satellite images to explore the spatial signature of the El Niño-Southern Oscillation signal in the Gulf of California. We used empirical orthogonal function analysis to extract the principal mode of the nonseasonal sea-surface temperature variability and compared it to the spatial signature of the Southern Oscillation Index. The first mode accounted for 80% of nonseasonal variability and its amplitude time series was significantly correlated to the Southern Oscillation Index (r = −0.58,P \u3c 0.01). The amplitude of this mode and its statistical relation to the El Niño is stronger during winter, which suggests that forcing of sea-surface temperature variability occurs through the disruption of the wind-driven upwelling corridor along the eastern coast due to El Niño-related atmospheric teleconnections. We also examined weekly time series of coastal sea-surface temperature coastal anomalies along the coast of North America, including the interior of the Gulf of California, during the strong 1997–98 El Niño. We found a poleward propagating signal that reached the mouth of the Gulf of California at the end of spring and continued its poleward propagation along the west coast of the peninsula slightly delayed; it also resulted in warming inside the Gulf of California. This observation may provide an explanation for the variable extension of the El Niño signature along the Pacific coast of North America
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