11,001 research outputs found
Surface-sensitive NMR in optically pumped semiconductors
We present a scheme of surface-sensitive nuclear magnetic resonance in
optically pumped semiconductors, where an NMR signal from a part of the surface
of a bulk compound semiconductor is detected apart from the bulk signal. It
utilizes optically oriented nuclei with a long spin-lattice relaxation time as
a polarization reservoir for the second (target) nuclei to be detected. It
provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond.
14, 1635 (2004)], which is a polarization reservoir at a surface of the
optically pumped semiconductor that polarizes nuclear spins in a target
material in contact through the nanostructured interfaces.Comment: 4 pages, 5 figure
Spatially resolved spectroscopy of the exoplanet HR 8799 c
HR 8799 is a multi-planet system detected in direct imaging, with three
companions known so far. Here, we present spatially resolved VLT/NACO
3.88--4.10 micron spectroscopy of the middle planet, HR 8799 c, which has an
estimated mass of ~10 Mjup, temperature of ~1100 K and projected separation of
38 AU. The spectrum shows some differences in the continuum from existing
theoretical models, particularly longwards of 4 microns, implying that detailed
cloud structure or non-equilibrium conditions may play an important role in the
physics of young exoplanetary atmospheres.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter
Nonabelian Gauge Theories on Noncommutative Spaces
In this paper, we describe a method for obtaining the nonabelian
Seiberg-Witten map for any gauge group and to any order in theta. The equations
defining the Seiberg-Witten map are expressed using a coboundary operator, so
that they can be solved by constructing a corresponding homotopy operator. The
ambiguities, of both the gauge and covariant type, which arise in this map are
manifest in our formalism.Comment: 14 pages, latex, Talk presented at 2001: A Spacetime Odyssey -
Michigan Center for Theoretical Physics, some typos correcte
Optical pumping NMR in the compensated semiconductor InP:Fe
The optical pumping NMR effect in the compensated semiconductor InP:Fe has
been investigated in terms of the dependences of photon energy (E_p), helicity
(sigma+-), and exposure time (tau_L) of infrared lights. The {31}P and {115}In
signal enhancements show large sigma+- asymmetries and anomalous oscillations
as a function of E_p. We find that (i) the oscillation period as a function of
E_p is similar for {31}P and {115}In and almost field independent in spite of
significant reduction of the enhancement in higher fields. (ii) A
characteristic time for buildup of the {31}P polarization under the light
exposure shows strong E_p-dependence, but is almost independent of sigma+-.
(iii) The buildup times for {31}P and {115}In are of the same order (10^3 s),
although the spin-lattice relaxation times (T_1) are different by more than
three orders of magnitude between them. The results are discussed in terms of
(1) discrete energy spectra due to donor-acceptor pairs (DAPs) in compensated
semiconductors, and (2) interplay between {31}P and dipolar ordered indium
nuclei, which are optically induced.Comment: 8 pages, 6 figures, submitted to Physical Review
Muon spin relaxation and rotation study on the solid solution of the two spin-gap systems (CH3)2CHNH3-CuCl3 and (CH3)2CHNH3-CuBr3
Muon-spin-rotation and relaxation studies have been performed on
(CH)CHNHCu(ClBr) with =0.85 and 0.95, which are
solid solutions of the two isomorphic spin-gap systems
(CH)CHNHCuCl and (CH)CHNHCuBr with different
spin gaps. The sample with =0.85 showed a clear muon spin rotation under
zero-field below =11.65K, indicating the existence of a long-range
antiferromagnetic order. A critical exponent of the hyperfine field was
obtained to be =0.33, which agrees with 3D-Ising model. In the other
sample with =0.95, an anomalous enhancement of the muon spin relaxation was
observed at very low temperatures indicating a critical slowing down due to a
magnetic instability of the ground state
On Bose-Einstein condensate inside moving exciton-phonon droplets
We explore a nonlinear field model to describe the interplay between the
ability of excitons to be Bose condensed and their interaction with other modes
of a crystal. We apply our consideration to the long-living paraexcitons in
Cu2O. Taking into account the exciton-phonon interaction and introducing a
coherent phonon part of the moving condensate, we solve quasi-stationary
equations for the exciton-phonon condensate. These equations support localized
solutions, and we discuss the conditions for the inhomogeneous condensate to
appear in the crystal. Allowable values of the characteristic width of
ballistic condensates are estimated. The stability conditions of the moving
condensate are analyzed by use of Landau arguments, and Landau critical
parameters appear in the theory. It follows that, under certain conditions, the
condensate can move through the crystal as a stable droplet. To separate the
coherent and non-coherent parts of the exciton-phonon packet, we suggest to
turn off the phonon wind by the changes in design of the 3D crystal and
boundary conditions for the moving droplet.Comment: 13 pages, LaTeX, three eps figures are incorporated by epsf.
submitted to Phys. Letters
Fundamental Vibrational Transitions of HCl Detected in CRL 2136
We would like to understand the chemistry of dense clouds and their hot cores
more quantitatively by obtaining more complete knowledge of the chemical
species present in them. We have obtained high-resolution infrared absorption
spectroscopy at 3-4 um toward the bright infrared source CRL 2136. The
fundamental vibration-rotation band of HCl has been detected within a dense
cloud for the first time. The HCl is probably located in the warm compact
circumstellar envelope or disk of CRL 2136. The fractional abundance of HCl is
(4.9-8.7)e-8, indicating that approximately 20 % of the elemental chlorine is
in gaseous HCl. The kinetic temperature of the absorbing gas is 250 K, half the
value determined from infrared spectroscopy of 13CO and water. The percentage
of chlorine in HCl is approximately that expected for gas at this temperature.
The reason for the difference in temperatures between the various molecular
species is unknown.Comment: 6 pages, 3 figures, A&A in pres
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