3,203 research outputs found
Nonlinear Hall effect as a signature of electronic phase separation in the semimetallic ferromagnet EuB6
This work reports a study of the nonlinear Hall Effect (HE) in the
semimetallic ferromagnet EuB6. A distinct switch in its Hall resistivity slope
is observed in the paramagnetic phase, which occurs at a single critical
magnetization over a wide temperature range. The observation is interpreted as
the point of percolation for entities of a more conducting and magnetically
ordered phase in a less ordered background. With an increasing applied magnetic
field, the conducting regions either increase in number or expand beyond the
percolation limit, hence increasing the global conductivity and effective
carrier density. An empirical two-component model expression provides excellent
scaling and a quantitative fit to the HE data and may be applicable to other
correlated electron systems.Comment: 15 Pages, 4 Figures. Accepted for publication in Phys. Rev. Let
Modulation of Noise in Submicron GaAs/AlGaAs Hall Devices by Gating
We present a systematic characterization of fluctuations in submicron Hall
devices based on GaAs/AlGaAs two-dimensional electron gas heterostructures at
temperatures between 1.5 K to 60 K. A large variety of noise spectra, from 1/f
to Lorentzian, are obtained by gating the Hall devices. The noise level can be
reduced by up to several orders of magnitude with a moderate gate voltage of
0.2 V, whereas the carrier density increases less than 60% in the same range.
The significant dependence of the Hall noise spectra on temperature and gate
voltage is explained in terms of the switching processes related to impurities
in n-AlGaAs.Comment: 5 pages, 4 fig
Large negative magnetoresistance in thiospinel CuCrZrS4
We report on large negative magnetoresistance observed in ferromagnetic
thiospinel compound CuCrZrS. Electrical resistivity increased with
decreasing temperature according to the form proportional to
, derived from variable range hopping with strong
electron-electron interaction. Resistivity under magnetic fields was expressed
by the same form with the characteristic temperature T0 decreasing with
increasing magnetic field. Magnetoresistance ratio is
1.5 at 100 K for H=90 kOe and increases divergently with decreasing temperature
reaching 80 at 16 K. Results of magnetization measurements are also presented.
Possible mechanism of the large magnetoresistance is discussed.Comment: 9 pages, 5 figures, to be published in Solid State Commu
Luminous X-ray AGN in Clusters of Galaxies
We present a study of X-ray AGN overdensities in 16 Abell clusters, within
the redshift range 0.073<z<0.279, in order to investigate the effect of the hot
inter-cluster environment on the triggering of the AGN phenomenon. The X-ray
AGN overdensities, with respect to the field expectations, were estimated for
sources with L_x>= 10^{42} erg s^{-1} (at the redshift of the clusters) and
within an area of 1 h^{-1}_{72} Mpc radius (excluding the core). To investigate
the presence or not of a true enhancement of luminous X-ray AGN in the cluster
area, we also derived the corresponding optical galaxy overdensities, using a
suitable range of -band magnitudes. We always find the latter to be
significantly higher (and only in two cases roughly equal) with respect to the
corresponding X-ray overdensities. Over the whole cluster sample, the mean
X-ray point-source overdensity is a factor of ~4 less than that corresponding
to bright optical galaxies, a difference which is significant at a >0.995
level, as indicated by an appropriate t-student test. We conclude that the
triggering of luminous X-ray AGN in rich clusters is strongly suppressed.
Furthermore, searching for optical SDSS counterparts of all the X-ray sources,
associated with our clusters, we found that about half appear to be background
QSOs, while others are background and foreground AGN or stars. The true
overdensity of X-ray point sources, associated to the clusters, is therefore
even smaller than what our statistical approach revealed.Comment: accepted for publication in ApJ Letter
Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO
TiO films were deposited on (100) Lanthanum aluminates
LaAlO substrates at a very low oxygen chamber pressure
mtorr employing a pulsed laser ablation deposition technique. In previous work,
it was established that the oxygen deficiency in these films induced
ferromagnetism. In this work it is demonstrated that this same oxygen
deficiency also gives rise to semiconductor titanium ion impurity donor energy
levels. Transport resistivity measurements in thin films of TiO
are presented as a function of temperature and magnetic field. Magneto- and
Hall- resistivity is explained in terms of electronic excitations from the
titanium ion donor levels into the conduction band.Comment: RevTeX4, Four pages, Four Figures in ^.eps forma
Ferromagnetism in (In,Mn)As Diluted Magnetic Semiconductor Thin Films Grown by Metalorganic Vapor Phase Epitaxy
In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown
using metalorganic vapor phase epitaxy (MOVPE).
Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source.
Nominally single-phase, epitaxial films were achieved with Mn content as high
as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and
higher Mn concentrations, nanometer scale MnAs precipitates were detected
within the In1-xMnxAs matrix. Magnetic properties of the films were
investigated using a superconducting quantum interference device (SQUID)
magnetometer. Room-temperature ferromagnetic order was observed in a sample
with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K
and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant
magnetization and the coercive field were small, with values of 10 emu/cm^3 and
400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is
discussed in light of the recent theory based on the formation of small
clusters of a few magnetic atoms.Comment: 5 pages, 5 figures, accepted for publication in JVST
Mechanistic and genetic basis of single-strand templated repair at Cas12a-induced DNA breaks in Chlamydomonas reinhardtii
Single-stranded oligodeoxynucleotides (ssODNs) are widely used as DNA repair templates inCRISPR/Cas precision genome editing. However, the underlying mechanisms of single-strandtemplated DNA repair (SSTR) are inadequately understood, constraining rational improve-ments to precision editing. Here we study SSTR at CRISPR/Cas12a-induced DNA double-strand breaks (DSBs) in the eukaryotic model green microalgaChlamydomonas reinhardtii.Wedemonstrate that ssODNs physically incorporate into the genome during SSTR at Cas12a-induced DSBs. This process is genetically independent of the Rad51-dependent homologousrecombination and Fanconi anemia pathways, is strongly antagonized by non-homologousend-joining, and is mediated almost entirely by the alternative end-joining enzyme poly-meraseθ. Thesefindings suggest differences in SSTR betweenC. reinhardtiiand animals. Ourwork illustrates the promising potentially ofC. reinhardtiias a model organism for studyingnuclear DNA repair
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