1,378 research outputs found
Experimental Setup for the Measurement of the Thermoelectric Power in Zero and Applied Magnetic Field
An experimental setup was developed for the measurement of the thermoelectric
power (TEP, Seebeck coefficient) in the temperature range from 2 to 350 K and
magnetic fields up to 140 kOe. The system was built to fit in a commercial
cryostat and is versatile, accurate and automated; using two heaters and two
thermometers increases the accuracy of the TEP measurement. High density data
of temperature sweeps from 2 to 350 K can be acquired in under 16 hours and
high density data of isothermal field sweeps from 0 to 140 kOe can be obtained
in under 2 hours. Calibrations for the system have been performed on a platinum
wire and BiSrCaCuO high superconductors.
The measured TEP of phosphor-bronze (voltage lead wire) turns to be very small,
where the absolute TEP value of phosphor-bronze wire is much less than 0.5
V/K below 80 K. For copper and platinum wires measured against to the
phosphor-bronze wire, the agreement between measured results and the literature
data is good. To demonstrate the applied magnetic field response of the system,
we report measurements of the TEP on single crystal samples of LaAgSb and
CeAgSb in fields up to 140 kOe.Comment: 10 pages, 8 figures. accepted in Measurement Science and Technolog
Two-Dimensional Nature of Four-Layer Superconductors by Inequivalent Hole Distribution
The magnetization of the four-layer superconductor
CuBa_{2}Ca_{3}Cu_4O_{12-\delta} with T_c\simeq117 K is presented. The
high-field magnetization around T_c(H) follows the exact two-dimensional
scaling function given by Te\v{s}anovi\'{c} and Andreev. This feature is
contrary to the inference that the interlayer coupling becomes strong if the
number of CuO_2 planes in a unit cell increases. Also, the fluctuation-induced
susceptibility in the low-field region was analyzed by using the modified
Lawrence-Doniach model. The effective number of independently fluctuating CuO_2
layers per unit cell, g_{\rm eff}, turned out to be \simeq 2 rather than 4,
which indicated that two among the four CuO_2 layers were in states far from
their optimal doping levels. This result could explain why
CuBa_{2}Ca_{3}Cu_4O_{12-\delta} shows two-dimensional behavior.Comment: 5 pages and 4 figure
Antiferromagnetic metal to heavy-fermion metal quantum phase transition in the Kondo lattice model: A strong coupling approach
We study the quantum phase transition from an antiferromagnetic metal to a
heavy fermion metal in the Kondo lattice model. Based on the strong coupling
approach we {\it first} diagonalize the Kondo coupling term. Since this strong
coupling approach makes the resulting Kondo term {\it relevant}, the Kondo
hybridization persists even in the antiferromagnetic metal, indicating that
fluctuations of Kondo singlets are not critical in the phase transition. We
find that the quantum transition in our strong coupling approach results from
{\it softening of antiferromagnetic spin fluctuations of localized spins},
driven by the Kondo interaction. Thus, the volume change of Fermi surface
becomes continuous across the transition. .....
Thermoelectric power of Ba(Fe1-xRux)2As2 and Ba(Fe1-xCox)2As2: possible changes of Fermi surface with and without changes in electron count
Temperature-dependent, in-plane, thermoelectric power (TEP) data are
presented for Ba(Fe1-xRux)2As2 (0 < x < 0.36) single crystals. The previously
outlined x - T phase diagram for this system is confirmed. The analysis of TEP
evolution with Ru-doping suggests significant changes in the electronic
structure, correlations and/or scattering occurring near ~7% and ~30% of
Ru-doping levels. These results are compared with an extended set of TEP data
for the electron-doped Ba(Fe1-xCox)2As2 series
Atom trapping with a thin magnetic film
We have created a Rb Bose-Einstein condensate in a magnetic trapping
potential produced by a hard disk platter written with a periodic pattern. Cold
atoms were loaded from an optical dipole trap and then cooled to BEC on the
surface with radiofrequency evaporation. Fragmentation of the atomic cloud due
to imperfections in the magnetic structure was observed at distances closer
than 40 m from the surface. Attempts to use the disk as an atom mirror
showed dispersive effects after reflection.Comment: 4 pages, 5 figure
The Infrared Einstein Ring in the Gravitational Lens MG1131+0456 and the Death of the Dusty Lens Hypothesis
We have obtained and modeled new NICMOS images of the lens system
MG1131+0456, which show that its lens galaxy is an H=18.6 mag, transparent,
early-type galaxy at a redshift of about z_l = 0.85; it has a major axis
effective radius R_e=0.68+/-0.05 arcsec, projected axis ratio b/a=0.77+/-0.02,
and major axis PA=60+/-2 degrees. The lens is the brightest member of a group
of seven galaxies with similar R-I and I-H colors, and the two closest group
members produce sufficient tidal perturbations to explain the ring morphology.
The host galaxy of the MG1131+0456 source is a z_s > 2 ERO (``extremely red
object'') which is lensed into optical and infrared rings of dramatically
different morphologies. These differences imply a strongly wavelength-dependent
source morphology that could be explained by embedding the host in a larger,
dusty disk. At 1.6 micron (H), the ring is spectacularly luminous, with a total
observed flux of H=17.4 mag and a de-magnified flux of 19.3 mag, corresponding
to a 1-2L_* galaxy at the probable source redshift of z_s > 2. Thus, it is
primarily the stellar emission of the radio source host galaxy that produces
the overall colors of two of the reddest radio lenses, MG1131+0456 and
B~1938+666, aided by the suppression of optical AGN emission by dust in the
source galaxy. The dusty lens hypothesis -- that many massive early-type
galaxies with 0.2 < z_l < 1.0 have large, uniform dust opacities -- is ruled
out.Comment: 27 pages, 8 COLOR figures, submitted to ApJ. Black and white version
available at http://cfa-www.harvard.edu/castle
Elastic constants of borocarbides. New approach to acoustic Measurement technique
A new version of the phase method of determining the sound velocity is
proposed and implemented. It utilizes the ``Nonius'' measurement technique and
can give acceptable accuracy (~1%) in samples of submillimeter size.
Measurements of the sound velocity are made in single-crystal samples of the
borocarbides RNi2B2C (R = Y,Lu,Ho). The elastic constants and the Debye
temperature are calculated.Comment: 5 figures, 2 table
Tuning Low Temperature Physical Properties of CeNiGe by Magnetic Field
We have studied the thermal, magnetic, and electrical properties of the
ternary intermetallic system CeNiGe by means of specific heat,
magnetization, and resistivity measurements. The specific heat data, together
with the anisotropic magnetic susceptibility, was analyzed on the basis of the
point charge model of crystalline electric field. The \,=\,5/2 multiplet of
the Ce is split by the crystalline electric field (CEF) into three
Kramers doublets, where the second and third doublet are separated from the
first (ground state) doublet by 100\,K and
170\,K, respectively. In zero field CeNiGe exhibits an
antiferromangeic order below = 5.0\,K. For
\textbf{H}\,\,\textbf{a} two metamagnetic transitions are clearly
evidenced between 2\,\,4\,K from the magnetization isotherm and extended
down to 0.4\,K from the magnetoresistance measurements. For
\textbf{H}\,\,\textbf{a}, shifts to lower temperature as
magnetic field increases, and ultimately disappears at
32.5\,kOe. For , the electrical resistivity shows the quadratic
temperature dependence (). For , an
unconventional -dependence of with emerges, the
exponent becomes larger as magnetic field increases. Although the
antiferromagnetic phase transition temperature in CeNiGe can be
continuously suppressed to zero, it provides an example of field tuning that
does not match current simple models of Quantum criticality.Comment: accepted PR
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