310 research outputs found
Observation of "Partial Coherence" in an Aharonov-Bohm Interferometer with a Quantum Dot
We report experiments on the interference through spin states of electrons in
a quantum dot (QD) embedded in an Aharonov-Bohm (AB) interferometer. We have
picked up a spin-pair state, for which the environmental conditions are ideally
similar and have traced the AB amplitude in the range of the gate voltage that
covers the pair. The behavior of the asymmetry in the amplitude around the two
Coulomb peaks agrees with the theoretical prediction that relates a spin-flip
process in a QD to the quantum dephasing of electrons. These results consist
evidence of "partial coherence" due to an entanglement of spins in the QD and
the interferometer.Comment: 4 pages, 3 figures, RevTe
Electrical coherent control of nuclear spins in a breakdown regime of quantum Hall effect
Using a conventional Hall-bar geometry with a micro-metal strip on top of the
surface, we demonstrate an electrical coherent control of nuclear spins in an
AlGaAs/GaAs semiconductor heterostructure. A breakdown of integer quantum Hall
(QH) effect is utilized to dynamically polarize nuclear spins. By applying a
pulse rf magnetic field with the metal strip, the quantum state of the nuclear
spins shows Rabi oscillations, which is detected by measuring longitudinal
voltage of the QH conductor.Comment: 3 pages, 4 figure
Dynamic nuclear polarization induced by breakdown of fractional quantum Hall effect
We study dynamic nuclear polarization (DNP) induced by breakdown of the
fractional quantum Hall (FQH) effect. We find that voltage-current
characteristics depend on current sweep rates at the quantum Hall states of
Landau level filling factors = 1, 2/3, and 1/3. The sweep rate dependence
is attributed to DNP occurring in the breakdown regime of FQH states. Results
of a pump and probe experiment show that the polarities of the DNP induced in
the breakdown regimes of the FQH states is opposite to that of the DNP induced
in the breakdown regimes of odd-integer quantum Hall states.Comment: 4 pages, 4 figure
On Optimal Leader’s Investments Strategy in a Cyclic Model of Innovation Race with Random Inventions Times
In this paper, we develop a new dynamic model of optimal investments in R&D and manufacturing for a technological leader competing with a large number of identical followers on the market of a technological product. The model is formulated in the form of the infinite time horizon stochastic optimization problem. The evolution of new generations of the product is treated as a Poisson-type cyclic stochastic process. The technology spillovers effect acts as a driving force of technological change. We show that the original probabilistic problem that the leader is faced with can be reduced to a deterministic one. This result makes it possible to perform analytical studies and numerical calculations. Numerical simulations and economic interpretations are presented as well
Universal zero-bias conductance for the single electron transistor. II: Comparison with numerical results
A numerical renormalization-group survey of the zero-bias electrical
conductance through a quantum dot embedded in the conduction path of a
nanodevice is reported. The results are examined in the light of a recently
derived linear mapping between the temperature-dependent conductance and the
universal function describing the conductance for the symmetric Anderson model.
A gate potential applied to the conduction electrons is known to change
markedly the transport properties of a quantum dot side-coupled to the
conduction path; in the embedded geometry here discussed, a similar potential
is shown to affect only quantitatively the temperature dependence of the
conductance. As expected, in the Kondo regime the numerical results are in
excellent agreement with the mapped conductances. In the mixed-valence regime,
the mapping describes accurately the low-temperature tail of the conductance.
The mapping is shown to provide a unified view of conduction in the
single-electron transistor.Comment: Sequel to arXiv:0906.4063. 9 pages with 8 figure
Evidence for a quantum-spin-Hall phase in graphene decorated with Bi2Te3 nanoparticles
Realization of the quantum-spin-Hall effect in graphene devices has remained
an outstanding challenge dating back to the inception of the field of
topological insulators. Graphene's exceptionally weak spin-orbit coupling
-stemming from carbon's low mass- poses the primary obstacle. We experimentally
and theoretically study artificially enhanced spin-orbit coupling in graphene
via random decoration with dilute Bi2Te3 nanoparticles. Remarkably,
multi-terminal resistance measurements suggest the presence of helical edge
states characteristic of a quantum-spin-Hall phase; the magnetic-field and
temperature dependence of the resistance peaks, X-ray photoelectron spectra,
scanning tunneling spectroscopy, and first-principles calculations further
support this scenario. These observations highlight a pathway to spintronics
and quantum-information applications in graphene-based quantum-spin-Hall
platforms
Evidence for a quantum-spin-Hall phase in graphene decorated with Bi_2Te_3 nanoparticles
Realization of the quantum spin Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene’s exceptionally weak spin-orbit coupling—stemming from carbon’s low mass—poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi_2Te_3 nanoparticles. Multiterminal resistance measurements suggest the presence of helical edge states characteristic of a quantum spin Hall phase; the magnetic field and temperature dependence of the resistance peaks, x-ray photoelectron spectra, scanning tunneling spectroscopy, and first-principles calculations further support this scenario. These observations highlight a pathway to spintronics and quantum information applications in graphene-based quantum spin Hall platforms
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