198 research outputs found
Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSeS
We report muon spin rotation (SR) and magnetization measurements under
pressure on FeSeS with x
.Above GPa we find microscopic coexistence of
superconductivity with an extended dome of long range magnetic order that spans
a pressure range between previously reported separated magnetic phases. The
magnetism initially competes on an atomic scale with the coexisting
superconductivity leading to a local maximum and minimum of the superconducting
. The maximum of corresponds to the onset of
magnetism while the minimum coincides with the pressure of strongest
competition. A shift of the maximum of for a series of single
crystals with x up to 0.14 roughly extrapolates to a putative magnetic and
superconducting state at ambient pressure for x .Comment: 10 pages, 6 figures, including supplemental materia
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Towards understanding edge localised mode mitigation by resonant magnetic perturbations in MAST
Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the
application of n = 3, 4 and 6 resonant magnetic perturbations (RMPs). For each
toroidal mode number of the non-axisymmetric applied fields, the frequency of
the ELMs has been increased significantly, and the peak heat flux on the
divertor plates reduced commensurately. This increase in ELM frequency occurs
despite a significant drop in the edge pressure gradient, which would be
expected to stabilise the peeling-ballooning modes thought to be responsible
for type-I ELMs. Various mechanisms which could cause a destabilisation of the
peeling-ballooning modes are presented, including pedestal widening, plasma
rotation braking, three dimensional corrugation of the plasma boundary and the
existence of radially extended lobe structures near to the X-point. This leads
to a model aimed at resolving the apparent dichotomy of ELM control, that is to
say ELM suppression occurring due to the pedestal pressure reduction below the
peeling-ballooning stability boundary, whilst the reduction in pressure can
also lead to ELM mitigation, which is ostensibly a destabilisation of
peeling-ballooning modes. In the case of ELM mitigation, the pedestal
broadening, 3d corrugation or lobes near the X-point degrade ballooning
stability so much that the pedestal recovers rapidly to cross the new stability
boundary at lower pressure more frequently, whilst in the case of suppression,
the plasma parameters are such that the particle transport reduces the edge
pressure below the stability boundary which is only mildly affected by
negligible rotation braking, small edge corrugation or short, broad lobe
structures.Comment: 23 pages, 12 figures. Copyright (2013) United Kingdom Atomic Energy
Authority. This article may be downloaded for personal use only. Any other
use requires prior permission of the author and the American Institute of
Physic
Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9
We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK
Analysis of test beam data taken with a prototype of TPC with resistive Micromegas for the T2K Near Detector upgrade
In this paper we describe the performance of a prototype of the High Angle
Time Projection Chambers (HA-TPCs) that are being produced for the Near
Detector (ND280) upgrade of the T2K experiment. The two HA-TPCs of ND280 will
be instrumented with eight Encapsulated Resistive Anode Micromegas (ERAM) on
each endplate, thus constituting in total 32 ERAMs. This innovative technique
allows the detection of the charge emitted by ionization electrons over several
pads, improving the determination of the track position. The TPC prototype has
been equipped with the first ERAM module produced for T2K and with the HA-TPC
readout electronics chain and it has been exposed to the DESY Test Beam in
order to measure spatial and dE/dx resolution. In this paper we characterize
the performances of the ERAM and, for the first time, we compare them with a
newly developed simulation of the detector response. Spatial resolution better
than 800 and dE/dx resolution better than 10% are observed for
all the incident angles and for all the drift distances of interest. All the
main features of the data are correctly reproduced by the simulation and these
performances fully fulfill the requirements for the HA-TPCs of T2K
Characterization of Charge Spreading and Gain of Encapsulated Resistive Micromegas Detectors for the Upgrade of the T2K Near Detector Time Projection Chambers
An upgrade of the near detector of the T2K long baseline neutrino oscillation
experiment is currently being conducted. This upgrade will include two new Time
Projection Chambers, each equipped with 16 charge readout resistive Micromegas
modules. A procedure to validate the performance of the detectors at different
stages of production has been developed and implemented to ensure a proper and
reliable operation of the detectors once installed. A dedicated X-ray test
bench is used to characterize the detectors by scanning each pad individually
and to precisely measure the uniformity of the gain and the deposited energy
resolution over the pad plane. An energy resolution of about 10% is obtained. A
detailed physical model has been developed to describe the charge dispersion
phenomena in the resistive Micromegas anode. The detailed physical description
includes initial ionization, electron drift, diffusion effects and the readout
electronics effects. The model provides an excellent characterization of the
charge spreading of the experimental measurements and allowed the simultaneous
extraction of gain and RC information of the modules
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