14,014 research outputs found
Slow light in paraffin-coated Rb vapor cells
We present preliminary results from an experimental study of slow light in
anti-relaxation-coated Rb vapor cells, and describe the construction and
testing of such cells. The slow ground state decoherence rate allowed by coated
cell walls leads to a dual-structured electromagnetically induced transparency
(EIT) spectrum with a very narrow (<100 Hz) transparency peak on top of a broad
pedestal. Such dual-structure EIT permits optical probe pulses to propagate
with greatly reduced group velocity on two time scales. We discuss ongoing
efforts to optimize the pulse delay in such coated cell systems.Comment: 6 pages, 6 figures, submitted to Journal of Modern Optic
Temperature and Kinematics of CIV Absorption Systems
We use Keck HIRES spectra of three intermediate redshift QSOs to study the
physical state and kinematics of the individual components of CIV selected
heavy element absorption systems. Fewer than 8 % of all CIV lines with column
densities greater than 10^{12.5} cm^{-2} have Doppler parameters b < 6 km/s. A
formal decomposition into thermal and non-thermal motion using the simultaneous
presence of SiIV gives a mean thermal Doppler parameter b_{therm}(CIV) = 7.2
km/s, corresponding to a temperature of 38,000 K although temperatures possibly
in excess of 300,000 K occur occasionally. We also find tentative evidence for
a mild increase of temperature with HI column density. Non-thermal motions
within components are typically small (< 10 km/s) for most systems, indicative
of a quiescent environment. The two-point correlation function (TPCF) of CIV
systems on scales up to 500 km/s suggests that there is more than one source of
velocity dispersion. The shape of the TPCF can be understood if the CIV systems
are caused by ensembles of objects with the kinematics of dwarf galaxies on a
small scale, while following the Hubble flow on a larger scale. Individual high
redshift CIV components may be the building blocks of future normal galaxies in
a hierarchical structure formation scenario.Comment: submitted to the ApJ Letters, March 16, 1996 (in press); (13 Latex
pages, 4 Postscript figures, and psfig.sty included
Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
Many-body interactions in transition-metal oxides give rise to a wide range
of functional properties, such as high-temperature superconductivity, colossal
magnetoresistance, or multiferroicity. The seminal recent discovery of a
two-dimensional electron gas (2DEG) at the interface of the insulating oxides
LaAlO3 and SrTiO3 represents an important milestone towards exploiting such
properties in all-oxide devices. This conducting interface shows a number of
appealing properties, including a high electron mobility, superconductivity,
and large magnetoresistance and can be patterned on the few-nanometer length
scale. However, the microscopic origin of the interface 2DEG is poorly
understood. Here, we show that a similar 2DEG, with an electron density as
large as 8x10^13 cm^-2, can be formed at the bare SrTiO3 surface. Furthermore,
we find that the 2DEG density can be controlled through exposure of the surface
to intense ultraviolet (UV) light. Subsequent angle-resolved photoemission
spectroscopy (ARPES) measurements reveal an unusual coexistence of a light
quasiparticle mass and signatures of strong many-body interactions.Comment: 14 pages, 4 figures, supplementary information (see other files
The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies
Although numerous simulations have been done to understand the effects of
intense bursts of star formation on high surface brightness galaxies, few
attempts have been made to understand how localized starbursts would affect
both the color and surface brightness of low surface brightness (LSB) galaxies.
To remedy this, we have run 53 simulations involving bursts of star formation
activity on LSB galaxies, varying both the underlying galaxy properties and the
parameters describing the starbursts. We discovered that although changing the
total color of a galaxy was fairly straightforward, it was virtually impossible
to alter a galaxy's central surface brightness and thereby remove it from the
LSB galaxy classification without placing a high (and fairly artificial)
threshold for the underlying gas density. The primary effect of large amounts
of induced star formation was to produce a centralized core (bulge) component
which is generally not observed in LSB galaxies. The noisy morphological
appearance of LSB galaxies as well as their noisy surface brightness profiles
can be reproduced by considering small bursts of star formation that are
localized within the disk. The trigger mechanism for such bursts is likely
distant/weak tidal encounters. The stability of disk central surface brightness
to these periods of star formation argues that the large space density of LSB
galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available
on http://guernsey.uoregon.edu/~kare
Filling of the Mott-Hubbard gap in the high temperature photoemission spectrum of (V_0.972Cr_0.028)_2O_3
Photoemission spectra of the paramagnetic insulating (PI) phase of
(V_0.972Cr_0.028)_2O_3, taken in ultra high vacuum up to the unusually high
temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH)
insulator and not observed previously. With increasing T the MH gap is filled
by spectral weight transfer, in qualitative agreement with high-T theoretical
calculations combining dynamical mean field theory and band theory in the local
density approximation.Comment: 4 pages, 4 figure
Photoemission study of (VM)O (M=Cr, Ti)
We present high-resolution bulk-sensitive photoemission spectra of
(VM)O (M=Cr, Ti). The measurements were made for the
paramagnetic metal (PM), paramagnetic insulator (PI), and antiferromagnetic
insulator (AFI) phases of (VM)O with the samples of =
0, 0.012, and 0.028 for Cr-doping and = 0.01 for Ti-doping. In the PM
phase, we observe a prominent quasiparticle peak in general agreement with
theory, which combines dynamical mean-field theory with the local density
approximation (LDA+DMFT). The quasiparticle peak shows a significantly larger
peak width and weight than in the theory. For both the PI and AFI phases, the
vanadium 3d parts of the valence spectra are not simple one peak structures.
For the PI phase, there is not yet a good theoretical understanding of these
structures. The size of the electron removal gap increases, and spectral weight
accumulates in the energy range closer to the chemical potential, when the PI
to AFI transition occurs. Spectra taken in the same phases with different
compositions show interesting monotonic changes as the dopant concentration
increases, regardless of the dopant species. With increased Cr-doping, the AFI
phase gap decreases and the PI phase gap increases.Comment: 13 pages, 16 figures. accepted for publication in Physical Review
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