Detection of a single-charge defect in a metal-oxide-semiconductor structure using vertically coupled Al and Si single-electron transistors

An Al-AlO_x-Al single-electron transistor (SET) acting as the gate of a narrow (~ 100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET) can induce a vertically aligned Si SET at the Si/SiO_2 interface near the MOSFET channel conductance threshold. By using such a vertically coupled Al and Si SET system, we have detected a single-charge defect which is tunnel-coupled to the Si SET. By solving a simple electrostatic model, the fractions of each coupling capacitance associated with the defect are extracted. The results reveal that the defect is not a large puddle or metal island, but its size is rather small, corresponding to a sphere with a radius less than 1 nm. The small size of the defect suggests it is most likely a single-charge trap at the Si/SiO_2 interface. Based on the ratios of the coupling capacitances, the interface trap is estimated to be about 20 nm away from the Si SET.Comment: 5 pages and 5 figure

Magnetic field-assisted manipulation and entanglement of Si spin qubits

Architectures of donor-electron based qubits in silicon near an oxide interface are considered theoretically. We find that the precondition for reliable logic and read-out operations, namely the individual identification of each donor-bound electron near the interface, may be accomplished by fine-tuning electric and magnetic fields, both applied perpendicularly to the interface. We argue that such magnetic fields may also be valuable in controlling two-qubit entanglement via donor electron pairs near the interface.Comment: 4 pages, 4 figures. 1 ref and 1 footnote adde

X-ray and low energy gamma-ray observations of the 16 February 1984 solar flare

The February 16, 1984 (0900 UT) solar flare was very energetic and produced a variety of emissions. The X-ray and gamma ray continuum measurement, made aboard the International Cometary Explorer (ICE) and the Pioneer Venus Orbiter (PVO), are briefly described

Nonlinear screening and ballistic transport in a graphene p-n junction

We study the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene. We show that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles. Accordingly, the junction resistance is lower than estimated in previous literature.Comment: 4 pages, 2 figures. (v1) Original version (v2) Introduction largely rewritten, minor typos fixed throughou

Magnetically-controlled impurities in quantum wires with strong Rashba coupling

We investigate the effect of strong spin-orbit interaction on the electronic transport through non-magnetic impurities in one-dimensional systems. When a perpendicular magnetic field is applied, the electron spin polarization becomes momentum-dependent and spin-flip scattering appears, to first order in the applied field, in addition to the usual potential scattering. We analyze a situation in which, by tuning the Fermi level and the Rashba coupling, the magnetic field can suppress the potential scattering. This mechanism should give rise to a significant negative magnetoresistance in the limit of large barriers.Comment: 4 pages, 2 figure

A brown dwarf orbiting an M-dwarf: MOA 2009–BLG–411L

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit. Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components. Results. We find that the source star is a giant G star with radius 9 R_⊙. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s^(-1). We find that the lens is composed of a brown dwarf secondary of mass M_S = 0.05 M_⊙ orbiting a primary M-star of mass M_P = 0.18 M_⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries. Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf

Quantum Hall line junction with impurities as a multi-slit Luttinger liquid interferometer

We report on quantum interference between a pair of counterpropagating quantum Hall edge states that are separated by a high quality tunnel barrier. Observed Aharonov-Bohm oscillations are analyzed in terms of resonant tunneling between coupled Luttinger liquids that creates bound electronic states between pairs of tunnel centers that act like interference slits. We place a lower bound in the range of 20-40 $\mu$m for the phase coherence length and directly confirm the extended phase coherence of quantum Hall edge states.Comment: 4 pages, 3 figures, 1 tabl