243 research outputs found
Normal state bottleneck and nematic fluctuations from femtosecond quasi-particle relaxation dynamics in Sm(Fe,Co)AsO
We investigate temperature and fluence dependent dynamics of the photoexcited
quasi-particle relaxation and low-energy electronic structure in electron-doped
1111-structure Sm(Fe_{0.93}Co_{0.07})AsO single crystal. We find that the
behavior is qualitatively identical to the 122-structure Ba(Fe,Co)_{2}As_{2}
including the presence of a normal state pseudogap and a marked 2-fold symmetry
breaking in the tetragonal phase that we relate to the electronic nematicity.
The 2-fold symmetry breaking appears to be a general feature of the electron
doped iron pnictides
Quasiparticle relaxation dynamics in spin-density-wave and superconducting SmFeAsO_{1-x}F_{x} single crystals
We investigate the quasiparticle relaxation and low-energy electronic
structure in undoped SmFeAsO and near-optimally doped SmFeAsO_{0.8}F_{0.2}
single crystals - exhibiting spin-density wave (SDW) ordering and
superconductivity respectively - using pump-probe femtosecond spectroscopy. In
the undoped single crystals a single relaxation process is observed, showing a
remarkable critical slowing down of the QP relaxation dynamics at the SDW
transition temperature T_{SDW}\simeq125{K}. In the superconducting (SC)
crystals multiple relaxation processes are present, with distinct SC state
quasiparticle recombination dynamics exhibiting a BCS-like T-dependent
superconducting gap, and a pseudogap (PG)-like feature with an onset above 180K
indicating the existence of a pseudogap of magnitude
2\Delta_{\mathrm{PG}}\simeq120 meV above T_{\mathrm{c}}. From the pump-photon
energy dependence we conclude that the SC state and PG relaxation channels are
independent, implying the presence of two separate electronic subsystems. We
discuss the data in terms of spatial inhomogeneity and multi-band scenarios,
finding that the latter is more consistent with the present data.Comment: Replaced by the correct versio
Meadow sage (Salvia pratensis L.): A neglected sage species with valuable phenolic compounds and biological potential
Inter-site pair superconductivity: origins and recent validation experiments
The challenge of understanding high-temperature superconductivity has led to
a plethora of ideas, but 30 years after its discovery in cuprates, very few
have achieved convincing experimental validation. While Hubbard and t-J models
were given a lot of attention, a number of recent experiments appear to give
decisive support to the model of real-space inter-site pairing and percolative
superconductivity in cuprates. Systematic measurements of the doping dependence
of the superfluid density show a linear dependence on superfluid density -
rather than doping - over the entire phase diagram, in accordance with the
model's predictions. The doping-dependence of the anomalous lattice dynamics of
in-plane Cu-O mode vibrations observed by inelastic neutron scattering, gives
remarkable reciprocal space signature of the inter-site pairing interaction
whose doping dependence closely follows the predicted pair density.
Symmetry-specific time-domain spectroscopy shows carrier localization, polaron
formation, pairing and superconductivity to be distinct processes occurring on
distinct timescales throughout the entire superconducting phase diagram. The
three diverse experimental results confirm non-trivial predictions made more
than a decade ago by the inter-site pairing model in the cuprates, remarkably
also confirming some of the fundamental notions mentioned in the seminal paper
on the discovery of high-temperature superconductivity in cuprates.Comment: Dedicated to Prof. K. A. Mueller on the Occasion of his 90th Birthda
Polaron and bipolaron transport in a charge segregated state of doped strongly correlated 2D semiconductor
The 2D lattice gas model with competing short and long range interactions is
appliedused for calculation of the incoherent charge transport in the classical
strongly-correlated charge segregated polaronic state. We show, by means of
Monte-Carlo simulations, that at high temperature the transport is dominated by
hopping of the dissociated correlated polarons, where with thetheir mobility is
inversely proportional to the temperature. At the temperatures below the
clustering transition temperature the bipolaron transport becomes dominant. The
energy barrier for the bipolaron hopping is determined by the Coulomb effects
and is found to be lower than the barrier for the single-polaron hopping. This
leads to drastically different temperature dependencies of mobilities for
polarons and bipolarons at low temperatures
Diamagnetism of real-space pairs above Tc in hole doped cuprates
The nonlinear normal state diamagnetism reported by Lu Li et al. [Phys. Rev.
B 81, 054510 (2010)] is shown to be incompatible with an acclaimed Cooper
pairing and vortex liquid above the resistive critical temperature. Instead it
is perfectly compatible with the normal state Landau diamagnetism of real-space
composed bosons, which describes the nonlinear magnetization curves in less
anisotropic cuprates La-Sr-Cu-O (LSCO) and Y-Ba-Cu-O (YBCO) as well as in
strongly anisotropic bismuth-based cuprates in the whole range of available
magnetic fields.Comment: 4 pages, 4 figure
Alchemilla Vulgaris L. kao potencijalni izvor prirodnih antioksidanata
The aim of this study was to examine the total phenolic and flavonoid content, and
antioxidant activity of the methanol extract of Alchemilla vulgaris aerial parts, as a
potential source of natural antioxidants. The obtained results showed that extract has high
total phenolic content (590,22 mg GAE/g), wheras flavonoid content was lower (12,58 mg
RU/g). Antioxidant activity was determined in vitro by DPPH· and ABTS+· reagents. The
IC50 values of DPPH (5,40 μg/ml) and ABTS+· scavenging capacities (60,10 μg/ml) of
methanol extract showed that tested extract has extremely strong antioxidant activity.Cilj ovog rada je bio ispitivanje antioksidativne aktivnosti, kao i koliÄŤine
ukupnih fenolnih jedinjenja i flavonoida u metanolnom ekstraktu biljke A. vulgaris L., kao
potencijalnog izvora prirodnih antioksidanata. Ispitivani ekstrakt poseduje visok sadrĹľaj
ukupnih fenola (590,22 mg GA/g), dok je koncentracija flavonoida znatno manja (12,58
mg RU/g). Antioksidativna aktivnost je ispitivana in vitro DPPH i ABTS+· metodom, a
IC50 vrednosti ukazuju da ispitivani ekstrakt pokazuje izuzetno visok stepen
antioksidativne aktivnosti u poređenju sa referentnim fenolnim jedinjenjima, što ukazuje
na mogućnost primene ekstrakta A. vulgaris u prehrambenoj industriji
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