1,830 research outputs found
Coexistence of a triplet nodal order-parameter and a singlet order-parameter at the interfaces of ferromagnet-superconductor Co/CoO/In junctions
We present differential conductance measurements of Cobalt / Cobalt-Oxide /
Indium planar junctions, 500nm x 500nm in size. The junctions span a wide range
of barriers, from very low to a tunnel barrier. The characteristic conductance
of all the junctions show a V-shape structure at low bias instead of the
U-shape characteristic of a s-wave order parameter. The bias of the conductance
peaks is, for all junctions, larger than the gap of indium. Both properties
exclude pure s-wave pairing. The data is well fitted by a model that assumes
the coexistence of s-wave singlet and equal spin p-wave triplet fluids. We find
that the values of the s-wave and p-wave gaps follow the BCS temperature
dependance and that the amplitude of the s-wave fluid increases with the
barrier strength.Comment: 5 pages, Accepted to Phys. Rev.
Influence of temperature dependent inelastic scattering on the superconducting proximity effect
We have measured the differential resistance of mesoscopic gold wires of
different lengths connected to an aluminum superconductor as a function of
temperature and voltage. Our experimental results differ substantially from
theoretical predictions which assume an infinite temperature independent gap in
the superconductor. In addition to taking into account the temperature
dependence of the gap, we must also introduce a temperature dependent inelastic
scattering length in order to fit our data
Shot noise measurements in NS junctions and the semiclassical theory
We present a new analysis of shot noise measurements in normal
metal-superconductor (NS) junctions [X. Jehl et al., Nature 405, 50 (2000)],
based on a recent semiclassical theory. The first calculations at zero
temperature assuming quantum coherence predicted shot noise in NS contacts to
be doubled with respect to normal contacts. The semiclassical approach gives
the first opportunity to compare data and theory quantitatively at finite
voltage and temperature. The doubling of shot noise is predicted up to the
superconducting gap, as already observed, confirming that phase coherence is
not necessary. An excellent agreement is also found above the gap where the
noise follows the normal case.Comment: 2 pages, revtex, 2 eps figures, to appear in Phys. Rev.
Spontaneous magnetization and Hall effect in superconductors with broken time-reversal symmetry
Broken time reversal symmetry (BTRS) in d wave superconductors is studied and
is shown to yield current carrying surface states. The corresponding
spontaneous magnetization is temperature independent near the critical
temperature Tc for weak BTRS, in accord with recent data. For strong BTRS and
thin films we expect a temperature dependent spontaneous magnetization with a
paramagnetic anomaly near Tc. The Hall conductance is found to vanish at zero
wavevector q and finite frequency w, however at finite q,w it has an unusual
structure.Comment: 7 pages, 1 eps figure, Europhysics Letters (in press
Towards understanding the variability in biospheric CO2 fluxes:Using FTIR spectrometry and a chemical transport model to investigate the sources and sinks of carbonyl sulfide and its link to CO2
Understanding carbon dioxide (CO2) biospheric processes is of great importance because the terrestrial exchange drives the seasonal and interannual variability of CO2 in the atmosphere. Atmospheric inversions based on CO2 concentration measurements alone can only determine net biosphere fluxes, but not differentiate between photosynthesis (uptake) and respiration (production). Carbonyl sulfide (OCS) could provide an important additional constraint: it is also taken up by plants during photosynthesis but not emitted during respiration, and therefore is a potential means to differentiate between these processes. Solar absorption Fourier Transform InfraRed (FTIR) spectrometry allows for the retrievals of the atmospheric concentrations of both CO2 and OCS from measured solar absorption spectra. Here, we investigate co-located and quasi-simultaneous FTIR measurements of OCS and CO2 performed at five selected sites located in the Northern Hemisphere. These measurements are compared to simulations of OCS and CO2 using a chemical transport model (GEOS-Chem). The coupled biospheric fluxes of OCS and CO2 from the simple biosphere model (SiB) are used in the study. The CO2 simulation with SiB fluxes agrees with the measurements well, while the OCS simulation reproduced a weaker drawdown than FTIR measurements at selected sites, and a smaller latitudinal gradient in the Northern Hemisphere during growing season when comparing with HIPPO (HIAPER Pole-to-Pole Observations) data spanning both hemispheres. An offset in the timing of the seasonal cycle minimum between SiB simulation and measurements is also seen. Using OCS as a photosynthesis proxy can help to understand how the biospheric processes are reproduced in models and to further understand the carbon cycle in the real world
quantum Heisenberg antiferromagnet on the triangular lattice: a group symmetry analysis of order by disorder
On the triangular lattice, for between and , the classical
Heisenberg model with first and second neighbor interactions presents
four-sublattice ordered ground-states. Spin-wave calculations of Chubukov and
Jolicoeur\cite{cj92} and Korshunov\cite{k93} suggest that quantum fluctuations
select amongst these states a colinear two-sublattice order. From theoretical
requirements, we develop the full symmetry analysis of the low lying levels of
the spin-1/2 Hamiltonian in the hypotheses of either a four or a two-sublattice
order. We show on the exact spectra of periodic samples ( and )
how quantum fluctuations select the colinear order from the four-sublattice
order.Comment: 15 pages, 4 figures (available upon request), Revte
Anomalous Fermi Liquid Behavior of Overdoped High-Tc Superconductors
According to a generic temperature vs. carrier-doping (T-p) phase diagram of
high-temperature superconductors it has been proposed that as doping increases
to the overdoped region they approach gradually a conventional (canonical)
Fermi Liquid. However, Hall effect measurements in several systems reported by
different authors show a still strong \emph{T}-dependence in overdoped samples.
We report here electrical transport measurements of
Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-delta} thin films presenting a temperature
dependence of the Hall constant, R_H, which does not present a gradual
transition towards the T-independent behavior of a canonical Fermi Liquid.
Instead, the T-dependence passes by a minimum near optimal doping and then
increases again in the overdoped region. We discuss the theoretical predictions
from two representative Fermi Liquid models and show that they can not give a
satisfactory explanation to our data. We conclude that this region of the phase
diagram in YBCO, as in most HTSC, is not a canonical Fermi Liquid, therefore we
call it Anomalous Fermi Liquid.Comment: 9 pages, 12 figures, to be published in Phys. Rev.
Epilogue: Superconducting Materials Past, Present and Future
Experimental contributors to the field of Superconducting Materials share
their informal views on the subject.Comment: Epilogue to Physica C Special Issue on Superconducting Materials,
Volume 514 (2015
Proximity Effect Enhancement Induced by Roughness of SN Interface
Critical temperature reduction is considered for a thin film of
a layered superconductor (S) with a rough surface covered by a thick layer of a
normal metal (N). The roughness of the SN interface increases the penetration
of electrons from the normal metal into the superconductor and leads to an
enhancement of the proximity effect. The value of induced by the
roughness of the SN interface can be much higher than for a film
with a plain surface for an extremely anisotropic layered superconductor with
the coherence lengths .Comment: 2 page
Evidence for a Bulk Complex Order-Parameter in Y0.9Ca0.1Ba2Cu3O7-delta Thin Films
We have measured the penetration depth of overdoped Y0.9Ca0.1Ba2Cu3O7-delta
(Ca-YBCO) thin films using two different methods. The change of the penetration
depth as a function of temperature has been measured using the parallel plate
resonator (PPR), while its absolute value was obtained from a quasi-optical
transmission measurements. Both sets of measurements are compatible with an
order parameter of the form: Delta*dx2-y2+i*delta*dxy, with Delta=14.5 +- 1.5
meV and delta=1.8 meV, indicating a finite gap at low temperature. Below 15 K
the drop of the scattering rate of uncondensed carriers becomes steeper in
contrast to a flattening observed for optimally doped YBCO films. This decrease
supports our results on the penetration depth temperature dependence. The
findings are in agreement with tunneling measurements on similar Ca-YBCO thin
films.Comment: 11 pages, 4 figure
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