32 research outputs found
History dependent magnetoresistance in lightly doped La_{2-x}Sr_{x}CuO_{4} thin films
The in-plane magnetoresistance (MR) in atomically smooth
La_{2-x}Sr_{x}CuO_{4} thin films grown by molecular-beam-epitaxy was measured
in magnetic fields B up to 9 T over a wide range of temperatures T. The films,
with x=0.03 and x=0.05, are insulating, and the positive MR emerges at T<4 K.
The positive MR exhibits glassy features, including history dependence and
memory, for all orientations of B. The results show that this behavior, which
reflects the onset of glassiness in the dynamics of doped holes, is a robust
feature of the insulating state.Comment: 4 pages, 4 figures, International School and Workshop on Electronic
Crystals (ECRYS-2011); to appear in Physica
Large Positive Magnetoresistance of the Lightly Doped La_{2}CuO_{4} Mott Insulator
The in-plane and out-of-plane magnetoresistance (MR) of single crystals of
La_2CuO_4, lightly doped (x=0.03) with either Sr (La_{2-x}Sr_xCuO_4) or Li
(La_2Cu_{1-x}Li_xO_4), have been measured in the fields applied parallel and
perpendicular to the CuO_2 planes. Both La_{1.97}Sr_{0.03}CuO_4 and
La_2Cu_{0.97}Li_{0.03}O_4 exhibit the emergence of a positive MR at
temperatures (T) well below the spin glass (SG) transition temperature T_{sg},
where charge dynamics is also glassy. This positive MR grows as T->0 and shows
hysteresis and memory. In this regime, the in-plane resistance R_{ab}(T,B) is
described by a scaling function, suggesting that short-range Coulomb repulsion
between two holes in the same disorder-localized state plays a key role at low
T. The results highlight similarities between this magnetic material and a
broad class of well-studied, nonmagnetic disordered insulators.Comment: 5+ pages, 3 figures; published versio
Skyrmions in a Doped Antiferromagnet
Magnetization and magnetoresistance have been measured in insulating
antiferromagnetic La_{2}Cu_{0.97}Li_{0.03}O_{4} over a wide range of
temperatures, magnetic fields, and field orientations. The magnetoresistance
step associated with a weak ferromagnetic transition exhibits a striking
nonmonotonic temperature dependence, consistent with the presence of skyrmions.Comment: 4+ pages, 3 figures (some low resolution), supplementary material (3
pages); discussion expanded, references added; as publishe
Evidence for Charge Glass-like Behavior in Lightly Doped La_{2-x}Sr_{x}CuO_{4} at Low Temperatures
A c-axis magnetotransport and resistance noise study in
La_{1.97}Sr_{0.03}CuO_{4} reveals clear signatures of glassiness, such as
hysteresis, memory, and slow, correlated dynamics, but only at temperatures (T)
well below the spin glass transition temperature T_{sg}. The results strongly
suggest the emergence of charge glassiness, or dynamic charge ordering, as a
result of Coulomb interactions.Comment: title changed, presentation improved, references added; to appear in
Phys. Rev. Letter
Upper critical fields and thermally-activated transport of Nd(O_0.7F_0.3)FeAs single crystal
We present measurements of the resistivity and the upper critical field H_c2
of Nd(O_0.7F_0.3)FeAs single crystals in strong DC and pulsed magnetic fields
up to 45 T and 60 T, respectively. We found that the field scale of H_c2 is
comparable to ~100 T of high T_c cuprates. H_c2(T) parallel to the c-axis
exhibits a pronounced upward curvature similar to what was extracted from
earlier measurements on polycrystalline samples. Thus this behavior is indeed
an intrinsic feature of oxypnictides, rather than manifestation of vortex
lattice melting or granularity. The orientational dependence of H_c2 shows
deviations from the one-band Ginzburg-Landau scaling. The mass anisotropy
decreases as T decreases, from 9.2 at 44K to 5 at 34K. Spin dependent
magnetoresistance and nonlinearities in the Hall coefficient suggest
contribution to the conductivity from electron-electron interactions modified
by disorder reminiscent that of diluted magnetic semiconductors. The Ohmic
resistivity measured below T_c but above the irreversibility field exhibits a
clear Arrhenius thermally activated behavior over 4-5 decades. The activation
energy has very different field dependencies for H||ab and H\perp ab. We
discuss to what extent different pairing scenarios can manifest themselves in
the observed behavior of H_{c2}, using the two-band model of superconductivity.
The results indicate the importance of paramagnetic effects on H_c2(T),which
may significantly reduce H_c2(0) as compared toH_c2(0)~200-300 T based on
extrapolations of H_c2(T) near T_c down to low temperatures.Comment: 11 pages, 16 figure
Azotobacter chroococcum F8/2: a multitasking bacterial strain in sugar beet biopriming
This study assesses the effects of Azotobacter biopriming on the early development of sugar beet. Azotobacter chroococcum F8/2 was screened for plant growth promoting characteristics and biopriming effects were estimated through germination parameters and the structural changes of the root tissues. A. chroococcum F8/2 was characterized as a contributor to nitrogen, iron, and potassium availability, as well as a producer of auxin and 1-aminocyclopropane-1-carboxilic acid deaminase. Applied biopriming had reduced mean germination time by 34.44% and increased vigor I by 90.99% compared to control. Volatile blend comprised 47.67% ethanol, 32.01% 2-methyl-propanol, 17.32% 3-methyl-1-butanol, and a trace of 2,3-butanedione. Root micromorphological analysis of bioprimed sugar beet revealed a considerable increase in primary, secondary xylem area, and vessels size. Obtained results determine A. chroococcum F8/2 as a successful biopriming agent, and active participant in nutrient availability and hormonal status modulation affecting root vascular tissue. Ā© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
Superstripes and complexity in high-temperature superconductors
While for many years the lattice, electronic and magnetic complexity of
high-temperature superconductors (HTS) has been considered responsible for
hindering the search of the mechanism of HTS now the complexity of HTS is
proposed to be essential for the quantum mechanism raising the superconducting
critical temperature. The complexity is shown by the lattice heterogeneous
architecture: a) heterostructures at atomic limit; b) electronic heterogeneity:
multiple components in the normal phase; c) superconducting heterogeneity:
multiple superconducting gaps in different points of the real space and of the
momentum space. The complex phase separation forms an unconventional granular
superconductor in a landscape of nanoscale superconducting striped droplets
which is called the "superstripes" scenario. The interplay and competition
between magnetic orbital charge and lattice fluctuations seems to be essential
for the quantum mechanism that suppresses thermal decoherence effects at an
optimum inhomogeneity.Comment: 20 pages, 3 figures; J. Supercon. Nov. Mag. 201
Theoretical assessment of phosphate amendments for stabilization of (Pb plus Zn) in polluted soil
Contamination of the environment with toxic metals, such as lead (Pb), represents a serious concern for human health. Most of the studies on Pb stabilization were performed using various phosphorus-containing amendments that can reduce Pb mobility and bioavailability by the sorption and precipitation of new, stable pyromorphite-type minerals, presenting very low solubility and bioaccessibility. However, the presence of competing ions, such as zinc (Zn), can reduce stabilization efficacy. The role of chemical composition on the stability of immobilization products of Pb and Zn by the addition of hydroxyapatite (HAP) Or fluoroapatite (FAP) has been examined in this paper. In this analysis we used a theoretical criterion which is based on calculation of the ion-ion interaction potential, representing the main term of the cohesive energy of the matrix/pollutant system. It has been demonstrated that the stability of the HAP matrix decreases and that the stability of the FAP matrix increases with the Pb immobilization in the presence of Zn. The results of this analysis point out FAIR as an advantageous amendment for the immobilization of Pb in the presence of Zn. (C) 2008 Elsevier Ltd. All rights reserved.1st International Conference on Environmental Management, Engineering, Planning and Economics (CEMEPE), Jun 24-28, 2007, Skiathos Isl, Greec