10,592 research outputs found
Phase-sensitive quantum effects in Andreev conductance of the SNS system of metals with macroscopic phase breaking length
The dissipative component of electron transport through the doubly connected
SNS Andreev interferometer indium (S)-aluminium (N)-indium (S) has been
studied. Within helium temperature range, the conductance of the individual
sections of the interferometer exhibits phase-sensitive oscillations of
quantum-interference nature. In the non-domain (normal) state of indium
narrowing adjacent to NS interface, the nonresonance oscillations have been
observed, with the period inversely proportional to the area of the
interferometer orifice. In the domain intermediate state of the narrowing, the
magneto-temperature resistive oscillations appeared, with the period determined
by the coherence length in the magnetic field equal to the critical one. The
oscillating component of resonance form has been observed in the conductance of
the macroscopic N-aluminium part of the system. The phase of the oscillations
appears to be shifted by compared to that of nonresonance oscillations.
We offer an explanation in terms of the contribution into Josephson current
from the coherent quasiparticles with energies of order of the Thouless energy.
The behavior of dissipative transport with temperature has been studied in a
clean normal metal in the vicinity of a single point NS contact.Comment: 9 pages, 7 figures, to be published in Low Temp. Phys., v. 29, No.
12, 200
Zero differential resistance in two-dimensional electron systems at large filling factors
We report on a state characterized by a zero differential resistance observed
in very high Landau levels of a high-mobility two-dimensional electron system.
Emerging from a minimum of Hall field-induced resistance oscillations at low
temperatures, this state exists over a continuous range of magnetic fields
extending well below the onset of the Shubnikov-de Haas effect. The minimum
current required to support this state is largely independent on the magnetic
field, while the maximum current increases with the magnetic field tracing the
onset of inter-Landau level scattering
Magnetotransport in a two-dimensional electron system in dc electric fields
We report on nonequilibrium transport measurements in a high-mobility
two-dimensional electron system subject to weak magnetic field and dc
excitation. Detailed study of dc-induced magneto-oscillations, first observed
by Yang {\em et al}., reveals a resonant condition that is qualitatively
different from that reported earlier. In addition, we observe dramatic
reduction of resistance induced by a weak dc field in the regime of separated
Landau levels. These results demonstrate similarity of transport phenomena in
dc-driven and microwave-driven systems and have important implications for
ongoing experimental search for predicted quenching of microwave-induced
zero-resistance states by a dc current.Comment: Revised version, to appear in Phys. Rev.
Implications of the X-ray Variability for the Mass of MCG-6-30-15
The bright Seyfert 1 galaxy \mcg shows large variability on a variety of time
scales. We study the \aproxlt 3 day time scale variability using a set of
simultaneous archival observations that were obtained from \rxte and the {\it
Advanced Satellite for Cosmology and Astrophysics} (\asca). The \rxte\
observations span nearly sec and indicate that the X-ray Fourier Power
Spectral Density has an rms variability of 16%, is flat from approximately
10^{-6} - 10^{-5} Hz, and then steepens into a power law
with \alpha\aproxgt 1. A further steepening to occurs
between 10^{-4}-10^{-3} Hz. The shape and rms amplitude are comparable to what
has been observed in \ngc and \cyg, albeit with break frequencies that differ
by a factor of 10^{-2} and 10^{4}, respectively. If the break frequencies are
indicative of the central black hole mass, then this mass may be as low as
. An upper limit of ks for the relative lag
between the 0.5-2 keV \asca band compared to the 8-15 keV \rxte band was also
found. Again by analogy with \ngc and \cyg, this limit is consistent with a
relatively low central black hole mass.Comment: 5 pages, 3 figures, LaTeX, uses emulateapj.sty and apjfonts.sty,
revised version, accepted for publication in ApJ Letter
The Origin of the Young Stars in the Nucleus of M31
The triple nucleus of M31 consists of a population of old red stars in an
eccentric disk (P1 and P2) and another population of younger A stars in a
circular disk (P3) around M31's central supermassive black hole (SMBH). We
argue that P1 and P2 determine the maximal radial extent of the younger A star
population and provide the gas that fueled the starburst that generated P3. The
eccentric stellar disk creates an non-axisymmetric perturbation to the
potential. This perturbed potential drives gas into the inner parsec around the
SMBH, if the pattern speed of the eccentric stellar disk is . We show that stellar mass loss from P1 and P2 is
sufficient to create a gravitationally unstable gaseous disk of \sim
10^5\Msun every Gyrs, consistent with the 200 Myr age of P3. Similar
processes may act in other systems to produce very compact nuclear starbursts.Comment: 10 pages, 7 figures, accepted by ApJ, changes made from referee
suggestion
Recommended from our members
Photoinduced Carrier Generation and Distribution in Solution-Deposited Titanyl Phthalocyanine Monolayers
Non-linear magnetotransport in microwave-illuminated two-dimensional electron systems
We study magnetoresistivity oscillations in a high-mobility two-dimensional
electron system subject to both microwave and dc electric fields. First, we
observe that the oscillation amplitude is a periodic function of the inverse
magnetic field and is strongly suppressed at microwave frequencies near
half-integers of the cyclotron frequency. Second, we obtain a complete set of
conditions for the differential resistivity extrema and saddle points. These
findings indicate the importance of scattering without microwave absorption and
a special role played by microwave-induced scattering events antiparallel to
the electric field.Comment: 4 pages, 4 figure
On the Antenna Beam Shape Reconstruction Using Planet Transit
The calibration of the in-flight antenna beam shape and possible
beamdegradation is one of the most crucial tasks for the upcoming Planck
mission. We examine several effects which could significantly influence the
in-flight main beam calibration using planet transit: the problems of the
variability of the Jupiter's flux, the antenna temperature and passing of the
planets through the main beam. We estimate these effects on the antenna beam
shape calibration and calculate the limits on the main beam and far sidelobe
measurements, using observations of Jupiter and Saturn. We also discuss
possible effects of degradation of the mirror surfaces and specify
corresponding parameters which can help us to determine these effects.Comment: 10 pages, 8 figure
Quantum Wall Crossing in N=2 Gauge Theories
We study refined and motivic wall-crossing formulas in N=2 supersymmetric
gauge theories with SU(2) gauge group and N_f < 4 matter hypermultiplets in the
fundamental representation. Such gauge theories provide an excellent testing
ground for the conjecture that "refined = motivic."Comment: 24 pages, 4 figure
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