4,449 research outputs found
Muon spin rotation and relaxation in the superconducting ferromagnet UCoGe
We report zero-field muon spin rotation and relaxation measurements on the
superconducting ferromagnet UCoGe. Weak itinerant ferromagnetic order is
detected by a spontaneous muon spin precession frequency below the Curie
temperature K. The precession frequency persists below the
bulk superconducting transition temperature K, where it measures
a local magnetic field T. The amplitude of the SR signal
provides unambiguous proof for ferromagnetism present in the whole sample
volume. We conclude ferromagnetism coexists with superconductivity on the
microscopic scale.Comment: 4 pages, 3 figures, accepted for publication in PR
Stratifying multiparameter persistent homology
A fundamental tool in topological data analysis is persistent homology, which
allows extraction of information from complex datasets in a robust way.
Persistent homology assigns a module over a principal ideal domain to a
one-parameter family of spaces obtained from the data. In applications data
often depend on several parameters, and in this case one is interested in
studying the persistent homology of a multiparameter family of spaces
associated to the data. While the theory of persistent homology for
one-parameter families is well-understood, the situation for multiparameter
families is more delicate. Following Carlsson and Zomorodian we recast the
problem in the setting of multigraded algebra, and we propose multigraded
Hilbert series, multigraded associated primes and local cohomology as
invariants for studying multiparameter persistent homology. Multigraded
associated primes provide a stratification of the region where a multigraded
module does not vanish, while multigraded Hilbert series and local cohomology
give a measure of the size of components of the module supported on different
strata. These invariants generalize in a suitable sense the invariant for the
one-parameter case.Comment: Minor improvements throughout. In particular: we extended the
introduction, added Table 1, which gives a dictionary between terms used in
PH and commutative algebra; we streamlined Section 3; we added Proposition
4.49 about the information captured by the cp-rank; we moved the code from
the appendix to github. Final version, to appear in SIAG
Possible Quantum Diffusion of Polaronic Muons in DyTiO Spin Ice
We interpret recent measurements of the zero field muon relaxation rate in
the frustrated magnetic pyrochlore DyTiO as resulting from the
quantum diffusion of muons in the substance. In this scenario, the plateau
observed at low temperature ( K) in the relaxation rate is due to coherent
tunneling of the muons through a spatially disordered spin state and not to any
magnetic fluctuations persisting at low temperature. Two further regimes either
side of a maximum relaxation rate at K correspond to a crossover
between tunnelling and incoherent activated hopping motion of the muon. Our fit
of the experimental data is compared with the case of muonium diffusion in KCl.Comment: 15 pages, 2 figure
Weak magnetism phenomena in heavy-fermion superconductors: selected SR studies
The behavior of the so-called weak moment antiferromagnetic states, observed
in the heavy-fermion superconductors UPt and URuSi, is discussed in
view of recent SR results obtained as function of control parameters like
chemical substitution and external pressure. In UPt, the Pd substitution
for Pt reveals the dynamical character of the weak moment order. On the other
hand, SR measurements performed on samples in which Th substitutes U
suggest that crystallographic disorder on the magnetic sites deeply affects the
fluctuation timescale. In URuSi, a phase separation between the
so-called hidden order state, present at ambient pressure, and an
antiferromagnetic state, occurring under pressure, is observed. In view of the
pressure-temperature phase diagram obtained by SR, it is deduced that the
respective order parameters have different symmetries.Comment: To appear in: J. Phys.: Cond. Matte
Spin dynamics in rare earth single molecule magnets from muSR and NMR in [TbPc] and [DyPc]
The spin dynamics in [TbPc] and [DyPc] single
molecule magnets have been investigated by means of muon and nuclear
spin-lattice relaxation rate measurements. The correlation time for the spin
fluctuations was found to be close to 0.1 ms already at 50 K, about two orders
of magnitude larger than the one previously found in other lanthanide based
single molecule magnets. In [TbPc] two different regimes for the
spin fluctuations have been evidenced: a high temperature activated one
involving spin fluctuations across a barrier separating
the ground and first excited states and a low temperature regime involving
quantum fluctuations within the twofold degenerate ground-state. In
[DyPc] a high temperature activated spin dynamics is also evidenced
which, however, cannot be explained in terms of a single spin-phonon coupling
constant.Comment: 4 pages, 4 figure
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Transforming Military Justice: The 2022 and 2023 National Defense Authorization Acts
For the past decade there have been numerous and significant changes to the Uniform Code of Military Justice (UCMJ), the statutory basis for the military justice system. Although the Military Justice Act of 2016 made major changes to the UCMJ, the calls for change continued. One of the most-often heard calls for reform over the last decade has suggested removing commanders from the military justice system. Some have argued that a command-centric military justice system was outdated, and it was time to make the system look more like the federal criminal procedure system. Other critics have advocated for a military justice system that looks more like those of our allied nations. In large part, those calls for reform were driven by the seemingly intractable problem of sexual assaults in the military. While there were other proposed changes to the UCMJ, calls for reducing the role of the commander took the lead
American Military Justice: Retaining the Commander\u27s Authority to Enforce Discipline and Justice
This white paper recommends that Congress reject proposals that would remove a commander’s prosecutorial discretion and instead place it in the hands of senior armed forces lawyers. There are currently two proposed legislative provisions that would adversely affect the commander’s prosecutorial discretion and undermine the commander’s ability to enforce good order and discipline. The first proposed provision was included in Section 540F of the 2020 National Defense Authorization Act, where Congress mandated that the Department of Defense report to the congressional armed services committees on the feasibility of creating a pilot program that would remove a commander’s authority to prefer, and refer to trial, court-martial charges for serious offenses and instead place that authority in the hands of senior armed forces lawyers
Magnetism in heavy-fermion U(Pt,Pd)3 studied by mSR
We report mSR experiments carried out on a series of heavy-electron
pseudobinary compounds U(Pt1-xPdx)3 (x<=0.05). For x<=0.005 the zero-field muon
depolarisation is described by the Kubo-Toyabe function. However the
temperature variation of the Kubo-Toyabe relaxation rate does not show any sign
of the small-moment antiferromagnetic phase with TN~6 K (signalled by neutron
diffraction), in contrast to previous reports. The failure to detect the small
ordered moment suggests it has a fluctuating (> 10 MHz) nature, which is
consistent with the interpretation of NMR data. For 0.01<=x<=0.05 the muon
depolarisation in the ordered state is described by two terms of equal
amplitude: an exponentially damped spontaneous oscillation and a Lorentzian
Kubo-Toyabe function. These terms are associated with antiferromagnetic order
with substantial moments. The Knight-shift measured in a magnetic field of 0.6
T on single-crystalline U(Pt0.95Pd0.05)3 in the paramagnetic state shows two
signals for B perpendicular to c, while only one signal is observed for B||c.
The observation of two signals for B perpendicular to c, while there is only
one muon localisation site (0,0,0), points to the presence of two spatially
distinct regions of different magnetic response.Comment: 25 pages including 12 figures (PS), J. Phys.: Condens. Matter, in
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