1,450 research outputs found
Upgrade of the Minos+ Experiment Data Acquisition for the High Energy NuMI Beam Run
The Minos+ experiment is an extension of the Minos experiment at a higher
energy and more intense neutrino beam, with the data collection having begun in
the fall of 2013. The neutrino beam is provided by the Neutrinos from the Main
Injector (NuMI) beam-line at Fermi National Accelerator Laboratory (Fermilab).
The detector apparatus consists of two main detectors, one underground at
Fermilab and the other in Soudan, Minnesota with the purpose of studying
neutrino oscillations at a base line of 735 km. The original data acquisition
system has been running for several years collecting data from NuMI, but with
the extended run from 2013, parts of the system needed to be replaced due to
obsolescence, reliability problems, and data throughput limitations.
Specifically, we have replaced the front-end readout controllers, event
builder, and data acquisition computing and trigger processing farms with
modern, modular and reliable devices with few single points of failure. The new
system is based on gigabit Ethernet TCP/IP communication to implement the event
building and concatenation of data from many front-end VME readout crates. The
simplicity and partitionability of the new system greatly eases the debugging
and diagnosing process. The new system improves throughput by about a factor of
three compared to the old system, up to 800 megabits per second, and has proven
robust and reliable in the current run.Comment: 3 page
Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by 75As NMR
We report As nuclear magnetic resonance (NMR) studies on a new
iron-based superconductor CaKFeAs with = 35 K. As
NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites
close to the K and Ca layers, respectively, revealing that K and Ca layers are
well ordered without site inversions. We found that nuclear quadrupole
frequencies of the As(1) and As(2) sites show an opposite
temperature () dependence. Nearly independent behavior of the Knight
shifts are observed in the normal state, and a sudden decrease in in
the superconducting (SC) state clearly evidences spin-singlet Cooper pairs.
As spin-lattice relaxation rates 1/ show a power law dependence
with different exponents for the two As sites. The isotropic antiferromagnetic
spin fluctuations characterized by the wavevector = (, 0) or (0,
) in the single-iron Brillouin zone notation are revealed by 1/ and
measurements. Such magnetic fluctuations are necessary to explain the
observed temperature dependence of the As quadrupole frequencies, as
evidenced by our first-principles calculations. In the SC state, 1/ shows
a rapid decrease below without a Hebel-Slichter peak and decreases
exponentially at low , consistent with an nodeless two-gap
superconductor.Comment: 9 pages, 6 figures, accepted for publication in Phys.Rev.
Thermodynamic insights into the intricate magnetic phase diagram of EuAl
The tetragonal intermetallic compound EuAl hosts an exciting variety of
low temperature phases. In addition to a charge density wave below 140 K, four
ordered magnetic phases are observed below 15.4 K. Recently, a skyrmion phase
was proposed based on Hall effect measurements under a -axis magnetic field.
We present a detailed investigation of the phase transitions in EuAl
under -axis magnetic field. Our dilatometry, heat capacity, DC magnetometry,
AC magnetic susceptibility, and resonant ultrasound spectroscopy measurements
reveal three magnetic phase transitions not previously reported. We discuss
what our results reveal about the character of the magnetic phases. Our first
key result is a detailed magnetic phase diagram mapping the
seven phases we observe. Second, we identify a new high-field phase, phase VII,
which directly corresponds to the region were skyrmions have been suggested.
Our results provide guidance for future studies exploring the complex magnetic
interactions and spin structures in EuAl.Comment: 20 pages, 15 figure
Real-space Visualization of Charge Density Wave Induced Local Inversion-Symmetry Breaking in a Skyrmion Magnet
Intertwining charge density wave (CDW) with spin and pairing order parameters
is a major focus of contemporary condensed matter physics. Lattice distortions
and local symmetry breaking resulted from CDWs are crucial for the emergence of
correlated and topological states in quantum materials in general. While the
presence of CDWs can be detected by diffraction or spectroscopic techniques,
atomic visualization of the CDW induced lattice distortions remains limited to
CDW with short wavelengths. In this letter, we realized the imaging of
incommensurate long-wavelength CDWs based on cryogenic four-dimensional
scanning transmission electron microscopy (cryo-4DSTEM). By visualizing the
incommensurate CDW induced lattice modulations in a skyrmion magnet EuAl4, we
discover two out-of-phase intra-unit cell shear modulations that specifically
break the local inversion-symmetry. Our results provide direct evidence for the
intertwined spin and charge orders in EuAl4 and key information about local
symmetry. Furthermore, we establish cryo-4DSTEM as an indispensable approach to
understand CDW induced new quantum states of matter
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