477 research outputs found
Superconductivity and magnetism in platinum-substituted SrFe2As2 single crystals
Single crystals of SrFe2-xPtxAs2 (0 < x < 0.36) were grown using the self
flux solution method and characterized using x-ray crystallography, electrical
transport, magnetic susceptibility, and specific heat measurements. The
magnetic/structural transition is suppressed with increasing Pt concentration,
with superconductivity seen over the range 0.08 < x < 0.36 with a maximum
transition temperature Tc of 16 K at x = 0.16. The shape of the phase diagram
and the changes to the lattice parameters are similar to the effects of other
group VIII elements Ni and Pd, however the higher transition temperature and
extended range of superconductivity suggest some complexity beyond the simple
electron counting picture that has been discussed thus far.Comment: 6 pages, 6 figure
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
Strong electron-boson coupling in the iron-based superconductor BaFe1.9Pt0.1As2 revealed by infrared spectroscopy
Understanding the formation of Cooper pairs in iron-based superconductors is
one of the most important topics in condensed matter physics. In conventional
superconductors, the electron-phonon interaction leads to the formation of
Cooper pairs. In conventional strong-coupling superconductors like lead (Pb),
the features due to electron-phonon interaction are evident in the infrared
absorption spectra. Here we investigate the infrared absorption spectra of the
iron arsenide superconductor BaFe1.9Pt0.1As2. We find that this superconductor
has fully gapped (nodeless) Fermi surfaces, and we observe the strong-coupling
electron-boson interaction features in the infrared absorption spectra. Through
modeling with the Eliashberg function based on Eliashberg theory, we obtain a
good quantitative description of the energy gaps and the strong-coupling
features. The full Eliashberg equations are solved to check the
self-consistency of the electron-boson coupling spectrum, the largest energy
gap, and the transition temperature (Tc). Our experimental data and analysis
provide compelling evidence that superconductivity in BaFe1.9Pt0.1As2 is
induced by the coupling of electrons to a low-energy bosonic mode that does not
originate solely from phonons.Comment: 9 pages, 5 figute
Fast method for the determination of short-chain-length polyhydroxyalkanoates (scl-PHAs) in bacterial samples by In Vial-Thermolysis (IVT)
none8siA new method based on the GC–MS analysis of thermolysis products obtained by treating bacterial
samples at a high temperature (above 270 C) has been developed. This method, here named “In-Vial-
Thermolysis” (IVT), allowed for the simultaneous determination of short-chain-length polyhydrox-
yalkanoates (scl-PHA) content and composition. The method was applied to both single strains and
microbial mixed cultures (MMC) fed with different carbon sources.
The IVT procedure provided similar analytical performances compared to previous Py-GC–MS and Py-
GC-FID methods, suggesting a similar application for PHA quantitation in bacterial cells. Results from the
IVT procedure and the traditional methanolysis method were compared; the correlation between the
two datasets was
fit for the purpose, giving a R2 of 0.975. In search of further simplification, the rationale
of IVT was exploited for the development of a “field method” based on the titration of thermolyzed
samples with sodium hydrogen carbonate to quantify PHA inside bacterial cells. The accuracy of the IVT
method was
fit for the purpose.
These results lead to the possibility for the on-line measurement of PHA productivity. Moreover, they
allow for the fast and inexpensive quantification/characterization of PHA for biotechnological process
control, as well as investigation over various bacterial communities and/or feeding strategies.mixedF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. Samorì; C. TorriF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. Samorì; C. Torr
Evolution of Structure and Superconductivity in Ba(NiCo)As
The effects of Co-substitution on Ba(NiCo)As () single crystals grown out of Pb flux are investigated via
transport, magnetic, and thermodynamic measurements. BaNiAs exhibits a
first order tetragonal to triclinic structural phase transition at
upon cooling, and enters a superconducting phase below . The
structural phase transition is sensitive to cobalt content and is suppressed
completely by . The superconducting critical temperature, ,
increases continuously with , reaching a maximum of at the
structural critical point and then decreases monotonically until
superconductivity is no longer observable well into the tetragonal phase. In
contrast to similar BaNiAs substitutional studies, which show an abrupt
change in at the triclinic-tetragonal boundary that extends far into the
tetragonal phase, Ba(NiCo)As exhibits a dome-like phase
diagram centered around the first-order critical point. Together with an
anomalously large heat capacity jump at optimal
doping, the smooth evolution of in the Ba(NiCo)As
system suggests a mechanism for pairing enhancement other than phonon
softening.Comment: 7 pages, 8 figure
On the resistivity at low temperatures in electron-doped cuprate superconductors
We measured the magnetoresistance as a function of temperature down to 20mK
and magnetic field for a set of underdoped PrCeCuO (x=0.12) thin films with
controlled oxygen content. This allows us to access the edge of the
superconducting dome on the underdoped side. The sheet resistance increases
with increasing oxygen content whereas the superconducting transition
temperature is steadily decreasing down to zero. Upon applying various magnetic
fields to suppress superconductivity we found that the sheet resistance
increases when the temperature is lowered. It saturates at very low
temperatures. These results, along with the magnetoresistance, cannot be
described in the context of zero temperature two dimensional
superconductor-to-insulator transition nor as a simple Kondo effect due to
scattering off spins in the copper-oxide planes. We conjecture that due to the
proximity to an antiferromagnetic phase magnetic droplets are induced. This
results in negative magnetoresistance and in an upturn in the resistivity.Comment: Accepted in Phys. Rev.
Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5
Heat and charge transport were used to probe the magnetic field-tuned quantum
critical point in the heavy-fermion metal CeCoIn. A comparison of
electrical and thermal resistivities reveals three characteristic energy
scales. A Fermi-liquid regime is observed below , with both transport
coefficients diverging in parallel and as , the
critical field. The characteristic temperature of antiferromagnetic spin
fluctuations, , is tuned to a minimum but {\it finite} value at ,
which coincides with the end of the -linear regime in the electrical
resistivity. A third temperature scale, , signals the formation of
quasiparticles, as fermions of charge obeying the Wiedemann-Franz law.
Unlike , it remains finite at , so that the integrity of
quasiparticles is preserved, even though the standard signature of Fermi-liquid
theory fails.Comment: 4 pages, 4 figures (published version
The Origin of Anomalous Low-Temperature Downturns in the Thermal Conductivity of Cuprates
We show that the anomalous decrease in the thermal conductivity of cuprates
below 300 mK, as has been observed recently in several cuprate materials
including PrCeCuO in the field-induced normal state,
is due to the thermal decoupling of phonons and electrons in the sample. Upon
lowering the temperature, the phonon-electron heat transfer rate decreases and,
as a result, a heat current bottleneck develops between the phonons, which can
in some cases be primarily responsible for heating the sample, and the
electrons. The contribution that the electrons make to the total low- heat
current is thus limited by the phonon-electron heat transfer rate, and falls
rapidly with decreasing temperature, resulting in the apparent low- downturn
of the thermal conductivity. We obtain the temperature and magnetic field
dependence of the low- thermal conductivity in the presence of
phonon-electron thermal decoupling and find good agreement with the data in
both the normal and superconducting states.Comment: 8 pages, 5 figure
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