31,064 research outputs found
Optical properties of TlNi2Se2: Observation of pseudogap formation
The quasi-two-dimensional nickel chalcogenides is a newly
discovered superconductor. We have performed optical spectroscopy study on
single crystals over a broad frequency range at various
temperatures. The overall optical reflectance spectra are similar to those
observed in its isostructure . Both the suppression in
and the peaklike feature in suggest the progressive
formation of a pseudogap feature in the midinfrared range with decreasing
temperatures, which might be originated from the dynamic local fluctuation of
charge-density-wave (CDW) instability. We propose that the CDW instability in
is driven by the saddle points mechanism, due to the existence of
van Hove singularity very close to the Fermi energy.Comment: 5 pages, 4 figure
A novel mechanism of charge density wave in a transition metal dichalcogenide
Charge density wave, or CDW, is usually associated with Fermi surfaces
nesting. We here report a new CDW mechanism discovered in a 2H-structured
transition metal dichalcogenide, where the two essential ingredients of CDW are
realized in very anomalous ways due to the strong-coupling nature of the
electronic structure. Namely, the CDW gap is only partially open, and charge
density wavevector match is fulfilled through participation of states of the
large Fermi patch, while the straight FS sections have secondary or negligible
contributions.Comment: 5 pages and 4 figure
Upper critical field and thermally activated flux flow in single crystalline TlRbFeSe
The upper critical field of
TlRbFeSe single crystals has been determined by
means of measuring the electrical resistivity in both a pulsed magnetic field
(60T) and a DC magnetic field (14T). It is found that
linearly increases with decreasing temperature for ,
reaching T. On the
other hand, a larger with a strong convex curvature
is observed for ((18K)60T). This compound shows a moderate anisotropy of the upper
critical field around , but decreases with decreasing temperature.
Analysis of the upper critical field based on the Werthamer-Helfand-Hohenberg
(WHH) method indicates that is orbitally limited for
, but the effect of spin paramagnetism may play an
important role on the pair breaking for . All these
experimental observations remarkably resemble those of the iron pnictide
superconductors, suggesting a unified scenario for the iron-based
superconductors. Moreover, the superconducting transition is significantly
broadened upon applying a magnetic field, indicating strong thermal fluctuation
effects in the superconducting state of
TlRbFeSe. The derived thermal activation energy
for vortex motion is compatible with those of the 1111-type iron pnictides.Comment: 7 pages, 6 figure
A Comparison of Quintessence and Nonlinear Born-Infeld Scalar Field Using Gold Supernova data
We study the Non-Linear Born-Infeld(NLBI) scalar field model and quintessence
model with two different potentials( and ). We
investigate the differences between those two models. We explore the equation
of state parameter w and the evolution of scale factor in both NLBI
scalar field and quintessence model. The present age of universe and the
transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to
constrain the parameters of the two models. All the results show that NLBI
model is slightly superior to quintessence model.Comment: 17 pages, 10 figures, some references adde
Two successive field-induced spin-flop transitions in single-crystalline CaCoAs
CaCoAs, a ThCrSi-structure compound, undergoes an
antiferromagnetic transition at \emph{T}=76K with the magnetic moments
being aligned parallel to the \emph{c} axis. Electronic transport measurement
reveals that the coupling between conducting carriers and magnetic order in
CaCoAs is much weaker comparing to the parent compounds of iron
pnictide. Applying magnetic field along \emph{c} axis induces two successive
spin-flop transitions in its magnetic state. The magnetization saturation
behaviors with \emph{\textbf{H}c} and \emph{\textbf{H}ab}
at 10K indicate that the antiferromagnetic coupling along \emph{c} direction is
very weak. The interlayer antiferromagntic coupling constant \emph{J} is
estimated to be about 2 meV.Comment: Accepted for publication in Phys. Rev. B. 5 pages, 6 figure
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