We have carried out {sup 63,65}Cu NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO{sub 2}. The ...measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.
Very high field super(29) Si-NMR measurements using a fully super(29) Si-enriched URu sub(2)Si sub(2) single crystal were carried out in order to microscopically investigate the "hidden order" (HO) ...state and adjacent magnetic phases in the high field limit. At the lowest measured temperature of 0.4 K, a clear anomaly reflecting a Fermi surface instability near 22 T inside the HO state is detected by the shift, super(29) K sub(c) Moreover, a strong enhancement of super(29) K sub(c)develops near a critical field H sub(c)Asymptotically = to 35.6 T, and the super(29)Si-NMR signal disappears suddenly at H sub(c) indicating the total suppression of the HO state. Nevertheless, a weak and shifted super(29)Si-NMR signal reappears for fields higher than H sub(c)at 4.2 K, providing evidence for a magnetic structure within the magnetic phase caused by the Ising-type anisotropy of the uranium ordered moments.
We examined how cytotoxic T lymphocyte antigen-4 (CTLA-4) regulates heterogeneous CD4+T cell responses by using experimental autoimmune encephalomyelitis (EAE), a CD4+T cell-mediated disease that is ...subject to regulation by CTLA-4. Disease incidence and severity were used as measures of in vivo CD4+T cell responses. The frequency, cytokine production, and reactivity of primed T cells were determined from animals immunized with proteolipid protein (PLP)-139-151 (disease agonist), PLP-Q (disease antagonist), or both peptides, and treated with control or anti-CTLA-4 antibody to analyze the responding population. CTLA-4 blockade exacerbated disease in PLP-139-151-primed animals and overcame disease antagonism in coimmunized animals, but did not permit disease induction in PLP-Q-primed animals. Experimental autoimmune encephalomyelitis enhancement was associated with increased frequencies of cytokine-producing cells and increased ratios of IFN-γ to IL-4 secretors responsive to PLP-139-151. Priming with PLP-Q elicited IL-4 and IL-2, but not IFN-γ secretors cross-reactive with PLP-139-151. Strikingly, CTLA-4 blockade was found to decrease rather than increase the frequencies of cross-reactive IL-4 and IL-2 secretors. Thus, CTLA-4 engagement limits the size, but increases the breadth, of reactivity of a primed pool of CD4+T cells, consequently regulating its function.
We have carried out super(63,65) Cu NMR spectra measurements in a magnetic field up to about 45 T on a single crystal of a multiferroic triangular antiferromagnet CuCrO sub(2). The measurements were ...performed for magnetic fields aligned along the crystal c axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H< or = 15 T). At higher fields magnetic structures form within individual triangular planes whereas the spin directions of the magnetic ions from neighboring planes are not correlated. It is established that the 2D-3D transition is hysteretic in field and temperature. Line-shape analysis reveals several possible magnetic structures existing within individual planes for different phases of CuCrO sub(2). Within certain regions on the magnetic H- T phase diagram of CuCrO sub(2) a 3D magnetic ordering with tensor order parameter is expected.
Photodarkening, or the shift of the optical absorption edge to smaller energies after excitation with light whose energy is near that of the optical band edge, has been studied in the chalcogenide ...glasses for many years. Authors have conducted high field NMR studies at 17 T and NQR studies of 75As in glassy As2S3. Authors have compared the 75As NMR and NQR lineshapes in glassy As2S3 and As2O3 before and after irradiation. An increase in the asymmetry parameter would have implied an increase in the departure from cylindrical symmetry in the bonding at the As pyramidal sites. The null result reported here is inconsistent with microscopic models of photodarkening that involve switching of large numbers of As chalcogen bonds. 16 refs.
Superconductivity appears in the cuprates when a spin order is destroyed, while the role of charge is less known. Recently, charge density wave (CDW) was found below the superconducting dome in YBa
...Cu
O
when a high magnetic field is applied perpendicular to the CuO
plane, which was suggested to arise from incipient CDW in the vortex cores that becomes overlapped. Here by
Cu-nuclear magnetic resonance, we report the discovery of CDW induced by an in-plane field, setting in above the dome in single-layered Bi
Sr
La
CuO
. The onset temperature T
takes over the antiferromagnetic order temperature T
beyond a critical doping level at which superconductivity starts to emerge, and scales with the pseudogap temperature T*. These results provide important insights into the relationship between spin order, CDW and the pseudogap, and their connections to high-temperature superconductivity.
Superconductivity appears in the cuprates when a spin order is destroyed, while the role of charge is less known. Recently, charge density wave (CDW) was found below the superconducting dome in ...YBa2Cu3O y when a high magnetic field is applied perpendicular to the CuO2 plane, which was suggested to arise from incipient CDW in the vortex cores that becomes overlapped. Here by 63Cu-nuclear magnetic resonance, we report the discovery of CDW induced by an in-plane field, setting in above the dome in single-layered Bi2Sr2−x La x CuO6. The onset temperature T CDW takes over the antiferromagnetic order temperature T N beyond a critical doping level at which superconductivity starts to emerge, and scales with the pseudogap temperature T*. These results provide important insights into the relationship between spin order, CDW and the pseudogap, and their connections to high-temperature superconductivity. Whilst superconductivity usually appears when magnetic order is suppressed, the role of charge is less known. Here, Kawasaki et al. report a charge density wave (CDW) above the superconducting transition induced by an in-plane magnetic field in Bi2Sr2-x La x CuO6, with the CDW onset temperature scaling with the pseudogap temperature.
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