422 research outputs found
Tunable Negative Differential Resistance controlled by Spin Blockade in Single Electron Transistors
We demonstrate a tunable negative differential resistance controlled by spin
blockade in single electron transistors. The single electron transistors
containing a few electrons and spin polarized source and drain contacts were
formed in GaAs/GaAlAs heterojunctions using metallic gates. Coulomb blockade
measurements performed as a function of applied source-drain bias, electron
number and magnetic field reveal well defined regimes where a decrease in the
current is observed with increasing bias. We establish that the origin of the
negative differential regime is the spin-polarized detection of electrons
combined with a long spin relaxation time in the dot. These results indicate
new functionalities that may be utilized in nano-spintronic devices in which
the spin state is electro-statically controlled via the electron occupation
number.Comment: 8 pages, 4 figure
The Collapse of the Spin-Singlet Phase in Quantum Dots
We present experimental and theoretical results on a new regime in quantum
dots in which the filling factor 2 singlet state is replaced by new spin
polarized phases. We make use of spin blockade spectroscopy to identify the
transition to this new regime as a function of the number of electrons. The key
experimental observation is a reversal of the phase in the systematic
oscillation of the amplitude of Coulomb blockade peaks as the number of
electrons is increased above a critical number. It is found theoretically that
correlations are crucial to the existence of the new phases.Comment: REVTeX4, 4 pages, 4 figures, to appear in PR
Electron spin manipulation and resonator readout in a double quantum dot nano-electromechanical system
Magnetically coupling a nano-mechanical resonator to a double quantum dot
confining two electrons can enable the manipulation of a single electron spin
and the readout of the resonator's natural frequency. When the Larmor frequency
matches the resonator frequency, the electron spin in one of the dots can be
selectively flipped by the magnetised resonator. By simultaneously measuring
the charge state of the two-electron double quantum dots, this transition can
be detected thus enabling the natural frequency of the mechanical resonator to
be determined.Comment: 7 pages, fixed typos, updated figures 4 and
Telegraph Noise in Coupled Quantum Dot Circuits Induced by a Quantum Point Contact
Charge detection utilizing a highly biased quantum point contact has become
the most effective probe for studying few electron quantum dot circuits.
Measurements on double and triple quantum dot circuits is performed to clarify
a back action role of charge sensing on the confined electrons. The quantum
point contact triggers inelastic transitions, which occur quite generally.
Under specific device and measurement conditions these transitions manifest
themselves as bounded regimes of telegraph noise within a stability diagram. A
nonequilibrium transition from artificial atomic to molecular behavior is
identified. Consequences for quantum information applications are discussed.Comment: 4 pages, 3 figures (as published
Spin-blockade spectroscopy of a two-level artificial molecule
Coulomb and spin blockade spectroscopy investigations have been performed on
an electrostatically defined ``artificial molecule'' connected to spin
polarized leads. The molecule is first effectively reduced to a two-level
system by placing both constituent atoms at a specific location of the level
spectrum. The spin sensitivity of the conductance enables us to identify the
electronic spin-states of the two-level molecule. We find in addition that the
magnetic field induces variations in the tunnel coupling between the two atoms.
The lateral nature of the device is evoked to explain this behavior.Comment: 4 pages, 4 figures; revised version with a minor change in Fig.2 and
additional inset in Fig.3.;accepted by PR
Coherent Manipulation of Individual Electron Spin in a Double Quantum Dot Integrated with a Micro-Magnet
We report the coherent manipulation of electron spins in a double quantum dot
integrated with a micro-magnet. We performed electric dipole spin resonance
experiments in the continuous wave (CW) and pump-and-probe modes. We observed
two resonant CW peaks and two Rabi oscillations of the quantum dot current by
sweeping an external magnetic field at a fixed frequency. Two peaks and
oscillations are measured at different resonant magnetic field, which reflects
the fact that the local magnetic fields at each quantum dot are modulated by
the stray field of a micro-magnet. As predicted with a density matrix approach,
the CW current is quadratic with respect to microwave (MW) voltage while the
Rabi frequency (\nu_Rabi) is linear. The difference between the \nu_Rabi values
of two Rabi oscillations directly reflects the MW electric field across the two
dots. These results show that the spins on each dot can be manipulated
coherently at will by tuning the micro-magnet alignment and MW electric field.Comment: 5 pages, 3 figure
The influence of the long-lived quantum Hall potential on the characteristics of quantum devices
Novel hysteretic effects are reported in magneto-transport experiments on
lateral quantum devices. The effects are characterized by two vastly different
relaxation times (minutes and days). It is shown that the observed phenomena
are related to long-lived eddy currents. This is confirmed by torsion-balance
magnetometry measurements of the same 2-dimensional electron gas (2DEG)
material. These observations show that the induced quantum Hall potential at
the edges of the 2DEG reservoirs influences transport through the devices, and
have important consequences for the magneto-transport of all lateral quantum
devices.Comment: 5 pages, 4 figure
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