18 research outputs found
ESR study of the spin ladder with uniform Dzyaloshinskii-Moria interaction
Evolution of the ESR absorption in a strong-leg spin ladder magnet
(CHN)CuBr (abbreviated as DIMPY) is studied from 300K to
400mK. Temperature dependence of the ESR relaxation follows a staircase of
crossovers between different relaxation regimes. We ague that the main
mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moria
interaction (K) with an effective longitudinal component along
an exchange bond of Cu ions within the legs resulting from the low crystal
symmetry of DIMPY and nontrivial orbital ordering. The same
Dzyaloshinskii-Moriya interaction results in the lifting of the triplet
excitation degeneracy, revealed through the weak splitting of the ESR
absorption at low temperatures.Comment: 13 pages, submitted to PRB, Fig.3 update
Symmetric and asymmetric excitations of a strong-leg quantum spin ladder
The zero-field excitation spectrum of the strong-leg spin ladder
(CHN)CuBr (DIMPY) is studied with a neutron time-of-flight
technique. The spectrum is decomposed into its symmetric and asymmetric parts
with respect to the rung momentum and compared with theoretical results
obtained by the density matrix renormalization group method. Additionally, the
calculated dynamical correlations are shown for a wide range of rung and leg
coupling ratios in order to point out the evolution of arising excitations, as
e.g. of the two-magnon bound state from the strong to the weak coupling limit
Long-lived magnons throughout the Brillouin zone of the strong-leg spin ladder (CHN)CuBr
Inelastic neutron scattering is used to measure spin excitations in fully
deuterated single crystal samples of the strong-leg antiferromagnetic S=1/2
spin ladder compound (CHN)CuBr. Sharp resolution-limited
magnons are observed across the entire one-dimensional Brillouin zone. The
results validate the previously proposed {\it symmetric} spin ladder model and
provide a reliable estimate of the relevant exchange interactions.Comment: 5 pages, 5 figure
Crystals for neutron scattering studies of quantum magnetism
We review a strategy for targeted synthesis of large single crystal samples
of prototype quantum magnets for inelastic neutron scattering experiments. Four
case studies of organic copper halogenide S=1/2 systems are presented. They are
meant to illustrate that exciting experimental results pertaining to forefront
many-body quantum physics can be obtained on samples grown using very simple
techniques, standard laboratory equipment, and almost no experience in in
advanced crystal growth techniques.Comment: 16 pages, 10 figure
Extracellular matrix-induced GM-CSF and hypoxia promote immune control of; Mycobacterium tuberculosis; in human; in vitro; granulomas
Several in vitro cellular models have been developed with the aim to reproduce and dissect human granulomatous responses, the hallmark of tuberculosis (TB) immunopathogenesis. In that context, we compared two- (2D) versus three-dimensional (3D) granuloma models resulting from infection of human peripheral blood mononuclear cells with M. tuberculosis (Mtb) in the absence or presence of a collagen-based extracellular matrix (ECM). Granuloma formation was found to be significantly enhanced in the 2D model. This feature was associated with an earlier chemokine production and lymphocyte activation, but also a significantly increased bacterial burden. Remarkably, the reduction in Mtb burden in the 3D model correlated with an increase in GM-CSF production. GM-CSF, which is known to promote macrophage survival, was found to be inherently induced by the ECM. We observed that only 3D in vitro granulomas led to the accumulation of lipid inclusions within Mtb. Our data suggest that a hypoxic environment within the ECM could be responsible for this dormant-like Mtb phenotype. Furthermore, exposure to a TNF-alpha antagonist reverted Mtb dormancy, thereby mimicking the reactivation of TB observed in rheumatic patients receiving this therapy. To conclude, we showed that only in vitro granulomas generated in the presence of an ECM could recapitulate some clinically relevant features of granulomatous responses in TB. As such, this model constitutes a highly valuable tool to study the interplay between immunity and Mtb stress responses as well as to evaluate novel treatment strategies
ESR study of the spin ladder with uniform Dzyaloshinskii-Moriya interaction
©2015 American Physical Society. Evolution of the ESR absorption in a strong-leg spin ladder magnet (C7H10N)2CuBr4 (abbreviated as DIMPY) is studied from 300 K to 400 mK. Temperature dependence of the ESR relaxation follows a staircase of crossovers between different relaxation regimes. We argue that the main mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moriya interaction (|D|=0.31 K) with an effective longitudinal component along an exchange bond of Cu ions within the legs resulting from the low crystal symmetry of DIMPY and nontrivial orbital ordering. The same Dzyaloshinskii-Moriya interaction along with other weaker anisotropic spin-spin interactions results in the lifting of the triplet excitation degeneracy, revealed through the weak splitting of the ESR absorption at low temperatures
ESR study of the spin ladder with uniform Dzyaloshinskii-Moriya interaction
©2015 American Physical Society. Evolution of the ESR absorption in a strong-leg spin ladder magnet (C7H10N)2CuBr4 (abbreviated as DIMPY) is studied from 300 K to 400 mK. Temperature dependence of the ESR relaxation follows a staircase of crossovers between different relaxation regimes. We argue that the main mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moriya interaction (|D|=0.31 K) with an effective longitudinal component along an exchange bond of Cu ions within the legs resulting from the low crystal symmetry of DIMPY and nontrivial orbital ordering. The same Dzyaloshinskii-Moriya interaction along with other weaker anisotropic spin-spin interactions results in the lifting of the triplet excitation degeneracy, revealed through the weak splitting of the ESR absorption at low temperatures
ESR study of the spin ladder with uniform Dzyaloshinskii-Moriya interaction
©2015 American Physical Society. Evolution of the ESR absorption in a strong-leg spin ladder magnet (C7H10N)2CuBr4 (abbreviated as DIMPY) is studied from 300 K to 400 mK. Temperature dependence of the ESR relaxation follows a staircase of crossovers between different relaxation regimes. We argue that the main mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moriya interaction (|D|=0.31 K) with an effective longitudinal component along an exchange bond of Cu ions within the legs resulting from the low crystal symmetry of DIMPY and nontrivial orbital ordering. The same Dzyaloshinskii-Moriya interaction along with other weaker anisotropic spin-spin interactions results in the lifting of the triplet excitation degeneracy, revealed through the weak splitting of the ESR absorption at low temperatures