4,136 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
Identification of nanoindentation-induced phase changes in silicon by in situ electrical characterization
In situ electrical measurements during nanoindentation of Czochralski grown p-type crystalline silicon (100) have been performed using a conducting diamond Berkovich indenter tip. Through-tip current monitoring with a sensitivity of ∼10pA and extraction of current-voltage curves at various points on the complete load-unload cycle have been used to track the phase transformations of silicon during the loading and unloading cycle. Postindent current-voltage curves prove to be extremely sensitive to phase changes during indentation, as well as to the final phase composition within the indented volume. For example, differences in the final structure are detected by current-voltage measurements even in an unloading regime in which only amorphous silicon is expected to form. The electrical measurements are interpreted with the aid of previously reported transmission electron microscopy and Raman microspectroscopy measurements.This work was funded by the Australian Research Council
and WRiota Pty Ltd
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
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
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
Charge qubits and limitations of electrostatic quantum gates
We investigate the characteristics of purely electrostatic interactions with
external gates in constructing full single qubit manipulations. The quantum bit
is naturally encoded in the spatial wave function of the electron system.
Single-electron{transistor arrays based on quantum dots or insulating
interfaces typically allow for electrostatic controls where the inter-island
tunneling is considered constant, e.g. determined by the thickness of an
insulating layer. A representative array of 3x3 quantum dots with two mobile
electrons is analyzed using a Hubbard Hamiltonian and a capacitance matrix
formalism. Our study shows that it is easy to realize the first quantum gate
for single qubit operations, but that a second quantum gate only comes at the
cost of compromising the low-energy two-level system needed to encode the
qubit. We use perturbative arguments and the Feshbach formalism to show that
the compromising of the two-level system is a rather general feature for
electrostatically interacting qubits and is not just related to the specific
details of the system chosen. We show further that full implementation requires
tunable tunneling or external magnetic fields.Comment: 7 pages, 5 figures, submitted to PR
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