585 research outputs found
External magnetic field effects on a distorted kagome antiferromagnet
We report bulk magnetization, and elastic and inelastic neutron scattering
measurements under an external magnetic field, , on the weakly coupled
distorted kagome system, Cu_{2}(OD)_3Cl. Our results show that the ordered
state below 6.7 K is a canted antiferromagnet and consists of large
antiferromagnetic -components and smaller ferromagnetic -components. By
first-principle calculations and linear spin wave analysis, we present a simple
spin hamiltonian with non-uniform nearest neighbor exchange interactions
resulting in a system of coupled spin trimers with a single-ion anisotropy that
can qualitatively reproduce the spin dynamics of Cu_{2}(OD)_3Cl.Comment: 5 figure
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
The application of a magnetic field transverse to the easy axis, Ising
direction in the quasi-two-dimensional Kagome staircase magnet, Co3V2O8,
induces three quantum phase transitions at low temperatures, ultimately
producing a novel high field polarized state, with two distinct sublattices.
New time-of-flight neutron scattering techniques, accompanied by large angular
access, high magnetic field infrastructure allow the mapping of a sequence of
ferromagnetic and incommensurate phases and their accompanying spin
excitations. At least one of the transitions to incommensurate phases at \mu
0Hc1~6.25 T and \mu 0Hc2~7 T is discontinuous, while the final quantum critical
point at \mu 0Hc3~13 T is continuous.Comment: 5 pages manuscript, 3 pages supplemental materia
Invasive pulmonary aspergillosis: effects of early resection in a neutropenic rat model
Objective: Invasive pulmonary aspergillosis is frequent in neutropenic patients. Usually localized in the beginning, the disease spreads and mortality is high despite antifungal treatment. The role of early adjuvant surgery is not clear. Surgery may help to confirm fungal disease, may control fungal disease locally and may prevent systemic spreading. This study examines effects of early resection on survival and dissemination in a rat model of localized invasive pulmonary aspergillosis. Methods: Forty persistently neutropenic male albino rats were challenged with standardized conidial aspergillus inoculum injected into peripheral lung tissue of the right upper lobe under direct vision. Animals were divided into four groups. Twenty animals were treated with amphotericin B at 1 mg/kg per day beginning 48 h after inoculation, 20 animals were left untreated. In each group half the animals underwent early resection of localized invasive aspergillosis by lobectomy. Animals were checked daily and mortality was recorded up to 28 days after which surviving animals were sacrificed. Results: Significantly higher survival was observed in resected animals in the non-Am B groups (survival: 10±19% without early resection and 50±32% with early resection; P=0.044). However, early resection did not lead to improved survival in animals treated with amphotericin B (survival 70±29% without early resection and 50±32% with early resection; P=0.316). Conclusions: In this rat model of localized invasive pulmonary aspergillosis effects of early resection on survival could be demonstrated only in animals not receiving amphotericin B treatmen
Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders
The weakly coupled quasi-one-dimensional spin ladder compound
(CH)CHNHCuCl is studied by neutron scattering in magnetic
fields exceeding the critical field of Bose-Einstein condensation of magnons.
Commensurate long-range order and the associated Goldstone mode are detected
and found to be similar to those in a reference 3D quantum magnet. However, for
the upper two massive magnon branches the observed behavior is totally
different, culminating in a drastic collapse of excitation bandwidth beyond the
transition point.Comment: 4 pages, 4 figure
Excitations in a four leg antiferromagnetic Heisenberg spin tube
Inelastic neutron scattering is used to investigate magnetic excitations in the quasi one dimensional quantum spin liquid system Cu2Cl4 D8C4SO2. Contrary to previously conjectured models that relied on bond alternating nearest neighbor interactions in the spin chains, the dominant interactions are actually next nearest neighbor in chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S 1 2 4 leg spin tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short range spin correlations
Inflection point in the magnetic field dependence of the ordered moment of URu2Si2 observed by neutron scattering in fields up to 17 T
We have measured the magnetic field dependence of the ordered
antiferromagnetic moment and the magnetic excitations in the heavy-fermion
superconductor URu2Si2 for fields up to 17 Tesla applied along the tetragonal c
axis, using neutron scattering. The decrease of the magnetic intensity of the
tiny moment with increasing field does not follow a simple power law, but shows
a clear inflection point, indicating that the moment disappears first at the
metamagnetic transition at ~40 T. This suggests that the moment m is connected
to a hidden order parameter Phi which belongs to the same irreducible
representation breaking time-reversal symmetry. The magnetic excitation gap at
the antiferromagnetic zone center Q=(1,0,0) increases continuously with
increasing field, while that at Q=(1.4,0,0) is nearly constant. This field
dependence is opposite to that of the gap extracted from specific-heat data.Comment: 10 pages, 5 figures, submitted to PR
Dominance of a clonal green sulfur bacterial population in a stratified lake
For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline (c. 8 × 106 GSB cells mL−1) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA, and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasio
Quantum spin liquid states in the two dimensional kagome antiferromagnets, ZnxCu4-x(OD)6Cl2
A three-dimensional system of interacting spins typically develops static
long-range order when it is cooled. If the spins are quantum (S = 1/2),
however, novel quantum paramagnetic states may appear. The most highly sought
state among them is the resonating valence bond (RVB) state in which every pair
of neighboring quantum spins form entangled spin singlets (valence bonds) and
the singlets are quantum mechanically resonating amongst all the possible
highly degenerate pairing states. Here we provide experimental evidence for
such quantum paramagnetic states existing in frustrated antiferromagnets,
ZnxCu4-x(OD)6Cl2, where the S = 1/2 magnetic Cu2+ moments form layers of a
two-dimensional kagome lattice. We find that in Cu4(OD)6Cl2, where distorted
kagome planes are weakly coupled to each other, a dispersionless excitation
mode appears in the magnetic excitation spectrum below ~ 20 K, whose
characteristics resemble those of quantum spin singlets in a solid state, known
as a valence bond solid (VBS), that breaks translational symmetry. Doping
nonmagnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens
the interplane coupling but also dilutes the magnetic occupancy of the kagome
lattice. The VBS state is suppressed and for ZnCu3(OD)6Cl2 where the kagome
planes are undistorted and 90% occupied by the Cu2+ ions, the low energy spin
fluctuations in the spin liquid phase become featureless
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