3,562 research outputs found
Giant Electron-hole Charging Energy Asymmetry in Ultra-short Carbon Nanotubes
Making full usage of bipolar transport in single-wall carbon nanotube (SWCNT)
transistors could permit the development of two-in-one quantum devices with
ultra-short channels. We report on clean 10 to 100 nm long suspended
SWCNT transistors which display a large electron-hole transport asymmetry. The
devices consist of naked SWCNT channels contacted with sections of
SWCNT-under-annealed-gold. The annealed gold acts as an n-doping top gate which
creates nm-sharp barriers at the junctions between the contacts and naked
channel. These tunnel barriers define a single quantum dot (QD) whose charging
energies to add an electron or a hole are vastly different ( charging
energy asymmetry). We parameterize the transport asymmetry by the ratio
of the hole and electron charging energies . We show that this
asymmetry is maximized for short channels and small band gap SWCNTs. In a small
band gap SWCNT device, we demonstrate the fabrication of a two-in-one quantum
device acting as a QD for holes, and a much longer quantum bus for electrons.
In a 14 nm long channel, reaches up to 2.6 for a device with a
band gap of 270 meV. This strong transport asymmetry survives even at
room temperature
Multi-frequency fine resolution imaging radar instrumentation and data acquisition
Development of a dual polarized L-band radar imaging system to be used in conjunction with the present dual polarized X-band radar is described. The technique used called for heterodyning the transmitted frequency from X-band to L-band and again heterodyning the received L-band signals back to X-band for amplification, detection, and recording
Constraining ^(26)Al+p resonances using ^(26)Al(^3He,d)^(27)Si
The ^(26)Al(^3He,d)^(27)Si reaction was measured from 0°≤θ_(c.m.)≤35° at E(^3He)=20 MeV using a quadrupole-dipole-dipole-dipole magnetic spectrometer. States in ^(27)Si were observed above the background at 7652 and 7741 keV and upper limits were set for the state at 7592 keV. Implications for the ^(26)Al(p,γ)^(27)Si stellar reaction rate are discussed
Charge Imbalance and Bilayer 2D Electron Systems at
We use interlayer tunneling to study bilayer 2D electron systems at over a wide range of charge density imbalance, ,
between the two layers. We find that the strongly enhanced tunneling associated
with the coherent excitonic phase at small layer separation can
survive at least up to an imbalance of = 0.5, i.e
= (3/4, 1/4). Phase transitions between the excitonic state and
bilayer states which lack significant interlayer correlations can be induced in
three different ways: by increasing the effective interlayer spacing ,
the temperature , or the charge imbalance, . We observe that
close to the phase boundary the coherent phase can be absent at
= 0, present at intermediate , but then absent again
at large , thus indicating an intricate phase competition between
it and incoherent quasi-independent layer states. At zero imbalance, the
critical shifts linearly with temperature, while at = 1/3
the critical is only weakly dependent on . At = 1/3 we
report the first observation of a direct phase transition between the coherent
excitonic bilayer integer quantum Hall phase and the pair of single
layer fractional quantized Hall states at = 2/3 and .Comment: 13 pages, 8 postscript figures. Final published versio
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