1,806 research outputs found
Kondo effect in a one-electron double quantum dot: Oscillations of the Kondo current in a weak magnetic field
We present transport measurements of the Kondo effect in a double quantum dot
charged with only one or two electrons, respectively. For the one electron case
we observe a surprising quasi-periodic oscillation of the Kondo conductance as
a function of a small perpendicular magnetic field |B| \lesssim 50mT. We
discuss possible explanations of this effect and interpret it by means of a
fine tuning of the energy mismatch of the single dot levels of the two quantum
dots. The observed degree of control implies important consequences for
applications in quantum information processing
An electrostatically defined serial triple quantum dot charged with few electrons
A serial triple quantum dot (TQD) electrostatically defined in a GaAs/AlGaAs
heterostructure is characterized by using a nearby quantum point contact as
charge detector. Ground state stability diagrams demonstrate control in the
regime of few electrons charging the TQD. An electrostatic model is developed
to determine the ground state charge configurations of the TQD. Numerical
calculations are compared with experimental results. In addition, the tunneling
conductance through all three quantum dots in series is studied. Quantum
cellular automata processes are identified, which are where charge
reconfiguration between two dots occurs in response to the addition of an
electron in the third dot.Comment: 12 pages, 9 figure
Mature natural killer cell and lymphoid tissue–inducing cell development requires Id2-mediated suppression of E protein activity
The Id2 transcriptional repressor is essential for development of natural killer (NK) cells, lymphoid tissue–inducing (LTi) cells, and secondary lymphoid tissues. Id2 was proposed to regulate NK and LTi lineage specification from multipotent progenitors through suppression of E proteins. We report that NK cell progenitors are not reduced in the bone marrow (BM) of Id2−/− mice, demonstrating that Id2 is not essential for NK lineage specification. Rather, Id2 is required for development of mature (m) NK cells. We define the mechanism by which Id2 functions by showing that a reduction in E protein activity, through deletion of E2A, overcomes the need for Id2 in development of BM mNK cells, LTi cells, and secondary lymphoid tissues. However, mNK cells are not restored in the blood or spleen of Id2−/−E2A−/− mice, suggesting a role for Id2 in suppression of alternative E proteins after maturation. Interestingly, the few splenic mNK cells in Id2−/− and Id2−/−E2A−/− mice have characteristics of thymus-derived NK cells, which develop in the absence of Id2, implying a differential requirement for Id2 in BM and thymic mNK development. Our findings redefine the essential functions of Id2 in lymphoid development and provide insight into the dynamic regulation of E and Id proteins during this process
Spin blockade in ground state resonance of a quantum dot
We present measurements on spin blockade in a laterally integrated quantum
dot. The dot is tuned into the regime of strong Coulomb blockade, confining ~
50 electrons. At certain electronic states we find an additional mechanism
suppressing electron transport. This we identify as spin blockade at zero bias,
possibly accompanied by a change in orbital momentum in subsequent dot ground
states. We support this by probing the bias, magnetic field and temperature
dependence of the transport spectrum. Weak violation of the blockade is
modelled by detailed calculations of non-linear transport taking into account
forbidden transitions.Comment: 4 pages, 4 figure
Spin-splitting in the quantum Hall effect of disordered GaAs layers with strong overlap of the spin subbands
With minima in the diagonal conductance G_{xx} and in the absolute value of
the derivative |dG_{xy}/dB| at the Hall conductance value G_{xy}=e^{2}/h,
spin-splitting is observed in the quantum Hall effect of heavily Si-doped GaAs
layers with low electron mobility 2000 cm^2/Vs in spite of the fact that the
spin-splitting is much smaller than the level broadening. Experimental results
can be explained in the frame of the scaling theory of the quantum Hall effect,
applied independently to each of the two spin subbands.Comment: 4 pages, 4 figure
Pseudo-spin Kondo effect versus hybridized molecular states in parallel Double Quantum Dots
A two quantum-dot device is coupled in parallel for studying the competition
between the pseudo-spin Kondo effect and strongly hybridized molecular states.
Cryogenic measurements are performed in the regime of weak coupling of the two
dots to lead states under linear transport conditions. Detailed simulations
verify the finding of the transition between the two different regimes.Comment: 14 pages, 3 figure
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