2,232 research outputs found
Very large spontaneous electric polarization in BiFeO3 single crystals at room temperature and its evolution under cycling fields
Electric polarization loops are measured at room temperature on highly pure
BiFeO3 single crystals synthesized by a flux growth method. Because the
crystals have a high electrical resistivity, the resulting low leakage currents
allow us to measure a large spontaneous polarization reaching 100
microC.cm^{-2}, a value never reported in the bulk. During electric cycling,
the slow degradation of the material leads to an evolution of the hysteresis
curves eventually preventing full saturation of the crystals.Comment: 8 pages, 3 figure
Macroeconomic Determinants of Liquidity of the Bond Market in Africa: Case Study of South Africa
The importance of the bond market to the financial system and broader economy of a country cannot be underestimated. Thus this study seeks to establish the determinants of liquidity in the South African bond market using monthly data covering the period 1995 to 2009, employing the Johansen cointegration test and the Vector Error Correction Model. Empirical results reveal that there is a longterm relationship between the selected macroeconomic variables and bond market liquidity in South Africa. Based on the empirical results, it is recommended that authorities should keep inflation at low and stables levels as well as a stable currency. Of great importance in the study is the role played by foreign investors in the bond market. The positive impact of the foreign investor participation on the bond market liquidity in South Africa suggests that authorities should remove restrictions on foreign investor activities to enhance liquidity in this important market
Doping dependence of the lattice dynamics in Ba(FeCo)As studied by Raman spectroscopy
We report Raman scattering spectra of iron-pnictide superconductor
Ba(FeCo)As single crystals with varying cobalt content.
Upon cooling through the tetragonal-to-orthorhombic transition, we observe a
large splitting of the E in-plane phonon modes involving Fe and As
displacements. The splitting of the in-plane phonons at the transition is
strongly reduced upon doping and disappears for qualitatively
following the trend displayed by the Fe magnetic moment. The origin of the
splitting is discussed in terms of magnetic frustration inherent to
iron-pnictide systems and we argue that such enhanced splitting may be linked
to strong spin-phonon coupling.Comment: 6 pages, 6 figure
Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(FeCo)As
We report a doping dependent electronic Raman scattering measurements on
iron-pnictide superconductor Ba(FeCo)As single crystals. A
strongly anisotropic gap is found at optimal doping for x=0.065 with
. Upon entering the coexistence region between
superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing
energy scale is strongly reduced. Our results are interpreted in terms of a
competition between SC and SDW orders for electronic state at the Fermi level.
Our findings advocate for a strong connection between the SC and SDW gaps
anisotropies which are both linked to interband interactions.Comment: 4 pages, 3 figure
The nodal gap component as a good candidate for the superconducting order parameter in cuprates
Although more than twenty years have passed since the discovery of high
temperature cuprate superconductivity, the identification of the
superconducting order parameter is still under debate. Here, we show that the
nodal gap component is the best candidate for the superconducting order
parameter. It scales with the critical temperature over a wide doping
range and displays a significant temperature dependence below in both the
underdoped and the overdoped regimes of the phase diagram. In contrast, the
antinodal gap component does not scale with in the underdoped side and
appears to be controlled by the pseudogap amplitude. Our experiments establish
the existence of two distinct gaps in the underdoped cuprates
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MGS accelerometer data analysis with the LMD GCM
Mars Global Surveyor aerobreaking phases, required to
achieve its mapping orbit, have yielded vertical profiles
of thermospheric densities, scale heights and temperatures
covering a broad range of local times, seasons and
spatial coordinates [Keating et al. 1998, 2001]. Phase
I covered local times from 11 to 16 h (assuming 24
"martian hours” per martian day or sols), with a latitude
coverage of approximately 40deg to 60deg N. Seasons
observed during this phase were centered around winter
solstice and altitudes of periapsis range from 115 to
135 km. The altitudes for Phase II were lower, with a
minimum around 100 km and a maximum around 120.
Martian spring was the season covered during this phase
and the local time was between 15 and 16 h. The latitude
covered by Phase II, however, was more extense
than that seen during Phase I, with a coverage from 60deg N
to basically the South Pole
Unconventional high-energy-state contribution to the Cooper pairing in under-doped copper-oxide superconductor HgBaCaCuO
We study the temperature-dependent electronic B1g Raman response of a
slightly under-doped single crystal HgBaCaCuO with a
superconducting critical temperature Tc=122 K. Our main finding is that the
superconducting pair-breaking peak is associated with a dip on its
higher-energy side, disappearing together at Tc. This result hints at an
unconventional pairing mechanism, whereas spectral weight lost in the dip is
transferred to the pair-breaking peak at lower energies. This conclusion is
supported by cellular dynamical mean-field theory on the Hubbard model, which
is able to reproduce all the main features of the B1g Raman response and
explain the peak-dip behavior in terms of a nontrivial relationship between the
superconducting and the pseudo gaps.Comment: 7 pages 4 figure
Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
High-resolution spectra of Pluto in the 1.66 um region, recorded with the
VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to
constrain the spatial and vertical distribution of methane in Pluto's
atmosphere and to search for mid-term (4 year) variability. A sensitivity study
to model assumptions (temperature structure, surface pressure, Pluto's radius)
is performed. Results indicate that (i) no variation of the CH4 atmospheric
content (column-density or mixing ratio) with Pluto rotational phase is present
in excess of 20 % (ii) CH4 column densities show at most marginal variations
between 2008 and 2012, with a best guess estimate of a ~20 % decrease over this
time frame. As stellar occultations indicate that Pluto's surface pressure has
continued to increase over this period, this implies a concomitant decrease of
the methane mixing ratio (iii) the data do not show evidence for an
altitude-varying methane distribution; in particular, they imply a roughly
uniform mixing ratio in at least the first 22-27 km of the atmosphere, and high
concentrations of low-temperature methane near the surface can be ruled out.
Our results are also best consistent with a relatively large (> 1180 km) Pluto
radius. Comparison with predictions from a recently developed global climate
model GCM indicates that these features are best explained if the source of
methane occurs in regional-scale CH4 ice deposits, including both low latitudes
and high Northern latitudes, evidence for which is present from the rotational
and secular evolution of the near-IR features due to CH4 ice. Our "best guess"
predictions for the New Horizons encounter in 2015 are: a 1184 km radius, a 17
ubar surface pressure, and a 0.44 % CH4 mixing ratio with negligible
longitudinal variations.Comment: 21 pages, 6 figure
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