2,226 research outputs found
The X-ray and radio emission from SN 2002ap: The importance of Compton scattering
The radio and X-ray observations of the Type Ic supernova SN 2002ap are
modeled. We find that inverse Compton cooling by photospheric photons explains
the observed steep radio spectrum, and also the X-ray flux observed by XMM.
Thermal emission from the shock is insufficient to explain the X-ray flux. The
radio emitting region expands with a velocity of, roughly, 70,000 km/s. From
the ratio of X-ray to radio emission we find that the energy densities of
magnetic fields and relativistic electrons are close to equipartion.Comment: 15 pages, 2 figures, ApJ accepte
Spin Inelastic Electron Tunneling Spectroscopy on Local Magnetic Moment Embedded in Josephson Junction
Recent experimental conductance measurements performed on paramagnetic
molecular adsorbates on a superconducting surface, using superconducting
scanning tunneling microscopy techniques, are theoretically investigated. For
low temperatures, we demonstrate that tunneling current assisted excitations of
the local magnetic moment cannot occur for voltage biases smaller than the
superconducting gap of the scanning tunneling microscope. The magnetic moment
is only excited for voltages corresponding to the sum of the superconducting
gap and the spin excitation energies. In excellent agreement with experiment,
we show that pumping into higher excitations give additional current signatures
by accumulation of density in the lower ones. Using external magnetic fields,
we Zeeman split possible degeneracy and thereby resolve all excitations
comprised in the magnetic moment.Comment: 6 pages, 4 figures, submitte
Electron Paramagnetic Resonance of Single Magnetic Moment on a Surface
We address electron spin resonance of single magnetic moments in a tunnel
junction using time-dependent electric fields and spin-polarized current. We
show that the tunneling current directly depends on the local magnetic moment
and that the frequency of the external electric field mixes with the
characteristic Larmor frequency of the local spin. The importance of the
spin-polarized current induced anisotropy fields acting on the local spin
moment is, moreover, demonstrated. Our proposed model thus explains the absence
of an electron spin resonance for a half integer spin, in contrast with the
strong signal observed for an integer spin.Comment: 6 pages, 2 figures, as publishe
Theory of spin-polarized scanning tunneling microscopy applied to local spins
We provide a theory for scanning tunneling microscopy and spectroscopy using
a spin-polarized tip. It it shown that the tunneling conductance can be
partitioned into three separate contributions, a background conductance which
is independent of the local spin, a dynamical conductance which is proportional
to the local spin moment, and a conductance which is proportional to the noise
spectrum of the local spin interactions. The presented theory is applicable to
setups with magnetic tip and substrate in non-collinear arrangement, as well as
for non-magnetic situations. The partitioning of the tunneling current suggests
a possibility to extract the total spin moment of the local spin from the
dynamical conductance. The dynamical conductance suggests a possibility to
generate very high frequency spin-dependent ac currents and/or voltages. We
also propose a measurement of the dynamical conductance that can be used to
determine the character of the effective exchange interaction between
individual spins in clusters. The third contribution to the tunneling current
is associated with the spin-spin correlations induced by the exchange
interaction between the local spin moment and the tunneling electrons. We
demonstrate how this term can be used in the analysis of spin excitations
recorded in conductance measurements. Finally, we propose to use spin-polarized
scanning tunneling microscopy for detailed studies of the spin excitation
spectrum.Comment: 12 pages, 4 figure, updated to match the published version, to appear
in the Phys. Rev.
Astrophysics in 2006
The fastest pulsar and the slowest nova; the oldest galaxies and the youngest
stars; the weirdest life forms and the commonest dwarfs; the highest energy
particles and the lowest energy photons. These were some of the extremes of
Astrophysics 2006. We attempt also to bring you updates on things of which
there is currently only one (habitable planets, the Sun, and the universe) and
others of which there are always many, like meteors and molecules, black holes
and binaries.Comment: 244 pages, no figure
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