18,700 research outputs found
Zero-field and Larmor spinor precessions in a neutron polarimeter experiment
We present a neutron polarimetric experiment where two kinds of spinor
precessions are observed: one is induced by different total energy of neutrons
(zero-field precession) and the other is induced by a stationary guide field
(Larmor precession). A characteristic of the former is the dependence of the
energy-difference, which is in practice tuned by the frequency of the
interacting oscillating magnetic field. In contrast the latter completely
depends on the strength of the guide field, namely Larmor frequency. Our
neutron-polarimetric experiment exhibits individual tuning as well as specific
properties of each spinor precession, which assures the use of both spin
precessions for multi-entangled spinor manipulation.Comment: 12 pages, 4 figure
Mechanism of Ambipolar Field-Effect Carrier Injections in One-Dimensional Mott Insulators
To clarify the mechanism of recently reported, ambipolar carrier injections
into quasi-one-dimensional Mott insulators on which field-effect transistors
are fabricated, we employ the one-dimensional Hubbard model attached to a
tight-binding model for source and drain electrodes. To take account of the
formation of Schottky barriers, we add scalar and vector potentials, which
satisfy the Poisson equation with boundary values depending on the drain
voltage, the gate bias, and the work-function difference. The current-voltage
characteristics are obtained by solving the time-dependent Schr\"odinger
equation in the unrestricted Hartree-Fock approximation. Its validity is
discussed with the help of the Lanczos method applied to small systems. We find
generally ambipolar carrier injections in Mott insulators even if the work
function of the crystal is quite different from that of the electrodes. They
result from balancing the correlation effect with the barrier effect. For the
gate-bias polarity with higher Schottky barriers, the correlation effect is
weakened accordingly, owing to collective transport in the one-dimensional
correlated electron systems.Comment: 21 pages, 10 figures, to appear in J. Phys. Soc. Jp
Kinematics of Red Variables in the Solar Neighborhood I. Basic Data Obtained by an SiO Maser Survey
In order to study the streaming motions of miras in the Solar neighborhood,
we newly surveyed 379 red variables in the SiO maser lines at 42.821 and 43.122
GHz with the Nobeyama 45m radio telescope. Accurate radial velocities were
obtained for 229 (220 new) detected stars. The sample is selected from optical
variables found by new automated surveys: the Northern Sky Variability Survey
and the All Sky Automated Survey. The new sample consists of the "bluer"
objects compared with those observed in the previous SiO surveys. The distances
to the objects are estimated using the period-luminosity relation, and they are
mostly less than 3 kpc from the Sun. The longitude-velocity diagram reveals
three prominent groups of stars deviant from the circular Galactic rotation
with a flat rotation curve. In addition to the Hercules group of stars which
was studied before, we found two new deviant groups: one toward the Perseus arm
and the other toward the Sagittarius arm. These two groups both exhibit
anomalous motions toward the Galactic center, which seem to be consistent with
the noncircular motions of these spiral arms found in the recent VLBI
proper-motion measurements for maser gas clumps.Comment: PASJ 64 no.1 (2012 Feb. 25 issue) in press. A full version including
Fig. 8a-m, and Fig. 9 are available at
http://www.nro.nao.ac.jp/~lib_pub/report/data/no680.pd
Signature of the transition to a bound state in thermoelectric quantum transport
We study a quantum dot coupled to two semiconducting reservoirs, when the dot
level and the electrochemical potential are both close to a band edge in the
reservoirs. This is modelled with an exactly solvable Hamiltonian without
interactions (the Fano-Anderson model). The model is known to show an abrupt
transition as the dot-reservoir coupling is increased into the strong-coupling
regime for a broad class of band structures. This transition involves an
infinite-lifetime bound state appearing in the band gap. We find a signature of
this transition in the continuum states of the model, visible as a
discontinuous behaviour of the dot's transmission function. This can result in
the steady-state DC electric and thermoelectric responses having a very strong
dependence on coupling close to critical coupling. We give examples where the
conductances and the thermoelectric power factor exhibit huge peaks at critical
coupling, while the thermoelectric figure of merit ZT grows as the coupling
approaches critical coupling, with a small dip at critical coupling. The
critical coupling is thus a sweet spot for such thermoelectric devices, as the
power output is maximal at this point without a significant change of
efficiency.Comment: 14 pages (10 figs) final version (a few typos corrected
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