43,739 research outputs found
A Measurement of Proper Motions of SiO Maser Sources in the Galactic Center with the VLBA
We report on the high-precision astrometric observations of maser sources
around the Galactic Center in the SiO J=1--0 v=1 and 2 lines with the VLBA
during 2001 -- 2004. With phase-referencing interferometry referred to the
radio continuum source Sgr A*, accurate positions of masers were obtained for
three detected objects: IRS 10 EE (7 epochs), IRS 15NE (2 epochs), and SiO 6
(only 1 epoch). Because circumstellar masers of these objects were resolved
into several components, proper motions for the maser sources were derived with
several different methods. Combining our VLBA results with those of the
previous VLA observations, we obtained the IRS 10EE proper motion of 76+-3 km
s^{-1} (at 8 kpc) to the south relative to Sgr A*. Almost null proper motion of
this star in the east--west direction results in a net transverse motion of the
infrared reference frame of about 30+-9 km s^{-1} to the west relative to Sgr
A*. The proper-motion data also suggests that IRS 10EE is an astrometric binary
with an unseen massive companion.Comment: High-res. figures are available at
ftp://ftp.nro.nao.ac.jp/nroreport/no656.pdf.gz . PASJ 60, No. 1 (2008) in
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Angle-resolved photoemission spectroscopy of perovskite-type transition-metal oxides and their analyses using tight-binding band structure
Nowadays it has become feasible to perform angle-resolved photoemission
spectroscopy (ARPES) measurements of transition-metal oxides with
three-dimensional perovskite structures owing to the availability of
high-quality single crystals of bulk and epitaxial thin films. In this article,
we review recent experimental results and interpretation of ARPES data using
empirical tight-binding band-structure calculations. Results are presented for
SrVO (SVO) bulk single crystals, and LaSrFeO (LSFO) and
LaSrMnO (LSMO) thin films. In the case of SVO, from comparison
of the experimental results with calculated surface electronic structure, we
concluded that the obtained band dispersions reflect the bulk electronic
structure. The experimental band structures of LSFO and LSMO were analyzed
assuming the G-type antiferromagnetic state and the ferromagnetic state,
respectively. We also demonstrated that the intrinsic uncertainty of the
electron momentum perpendicular to the crystal surface is important for the
interpretation of the ARPES results of three-dimensional materials.Comment: 25 pages, 12 figure
Experimental evidence for a two-gap structure of superconducting NbSe_2: a specific heat study in external magnetic fields
To resolve the discrepancies of the superconducting order parameter in
quasi-two-dimensional NbSe_2, comprehensive specific-heat measurements have
been carried out. By analyzing both the zero-field and mixed-state data with
magnetic fields perpendicular to and parallel to the c axis of the crystal and
using the two-gap model, we conclude that (1) more than one energy scale of the
order parameter is required for superconducting NbSe_2 due to the thermodynamic
consistency; (2)delta_L=1.26 meV and delta_S=0.73 meV are obtained; (3)
N_S(0)/N(0)=11%~20%; (4) The observation of the kink in gamma(H) curve suggests
that the two-gap scenario is more favorable than the anisotropic s-wave model
to describe the gap structure of NbSe_2; and (5)delta_S is more isotropic and
has a three-dimensional-like feature and is located either on the Se or the
bonding Nb Fermi sheets.Comment: 16 pages, 4 figure
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