517 research outputs found
Parity-broken ground state for the spin-1 pyrochlore antiferromagnet
The ground-state properties of the spin-1 pyrochlore antiferromagnet are
studied by applying the VBS-like tetrahedron-unit decomposition to the original
spin system. The symmetrization required on every vertex is taken into account
by introducing a ferromagnetic coupling. The pairwise effective Hamiltonian
between the adjacent tetrahedrons is obtained by considering the next nearest
neighbor and the third neighbor exchange interactions. We find that the
transverse component of the spin chirality exhibits a long-range order,
breaking the parity symmetry of the tetrahedral group, while the chirality
itself is not broken.Comment: 4 pages, 3 figures, REVTeX(ver.3.1
Pressure-induced changes in the magnetic and valence state of EuFe2As2
We present the results of electrical resistivity, ac specific heat, magnetic
susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular
dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under
pressure. Applying pressure leads to a continuous suppression of the
antiferromagnetism associated with Fe moments and the antiferromagnetic
transition temperature becomes zero in the vicinity of a critical pressure Pc
~2.5-2.7 GPa. Pressure-induced re-entrant superconductivity, which is highly
sensitive to the homogeneity of the pressure, only appears in the narrow
pressure region in the vicinity of Pc due to the competition between
superconductivity and the antiferromagnetic ordering of Eu2+ moments. The
antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state
above 6 GPa. We also found that the ferromagnetic order is suppressed with
further increasing pressure, which is connected with a valence change of Eu
ions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Berry phase in Magnetic Superconductors
In magnetic systems, electronic bands often acquire nontrivial topological
structure characterized by gauge flux distribution in momentum (k)-space. It
sometimes follows that the phase of the wavefunctions cannot be defined
uniquely over the whole Brillouin zone. In this Letter we develop a theory of
superconductivity in the presence of this gauge flux both in two- and
three-dimensional systems. It is found that the superconducting gap has "nodes"
as a function of k where the Fermi surface is penetrated by a gauge string.Comment: 4 pages, 3 figures, substantial changes in the presentation, to be
published in Phys. Rev. Let
Quantized Anomalous Hall Effect in Two-Dimensional Ferromagnets - Quantum Hall Effect from Metal -
We study the effect of disorder on the anomalous Hall effect (AHE) in
two-dimensional ferromagnets. The topological nature of AHE leads to the
integer quantum Hall effect from a metal, i.e., the quantization of
induced by the localization except for the few extended states
carrying Chern number. Extensive numerical study on a model reveals that
Pruisken's two-parameter scaling theory holds even when the system has no gap
with the overlapping multibands and without the uniform magnetic field.
Therefore the condition for the quantized AHE is given only by the Hall
conductivity without the quantum correction, i.e., .Comment: 5 pages, 4 figures, REVTe
NaIrO3 - A pentavalent post-perovskite
Sodium iridium(V) oxide, NaIrO3, was synthesized by a high pressure solid
state method and recovered to ambient conditions. It is found to be
isostructural with CaIrO3, the much-studied structural analogue of the
high-pressure post-perovskite phase of MgSiO3. Among the oxide
post-perovskites, NaIrO3 is the first example with a pentavalent cation. The
structure consists of layers of corner- and edge-sharing IrO6 octahedra
separated by layers of NaO8 bicapped trigonal prisms. NaIrO3 shows no magnetic
ordering and resistivity measurements show non-metallic behavior. The crystal
structure, electrical and magnetic properties are discussed and compared to
known post-perovskites and pentavalent perovskite metal oxides.Comment: 22 pages, 5 figures. Submitted to Journal of Solid State Chemistr
Gallinitiation enhances the availability of food resources for herbivorous insects
Summary 1. Insect herbivory may have not only negative but also positive plant-mediated effects on other insect herbivores. We investigated plant-mediated effects of the stem gall midge Rabdophaga rigidae on other insect herbivores through regrowth response of the willow Salix eriocarpa. 2. Gall initiation on current-year shoots stimulated the development of lateral shoots, followed by a secondary leaf flush. Lateral shoots and upper leaves on galled shoots were less tough and had a higher water and nitrogen content. 3. Colonization rates by the aphid Aphis farinosa were significantly higher on galled shoots than on ungalled shoots, because this aphid frequently colonized lateral shoots. 4. Adults of two leaf beetles, Plagiodera versicolora and Smaragdina semiaurantiaca , were more abundant on galled than on ungalled shoots; they preferentially fed on young leaves produced during the secondary leaf flush. 5. Gall initiation positively affected aphids and leaf beetles by enhancing the availability of food resources as a result of the regrowth responses of S. eriocarpa . This indicates that the regrowth responses of plants to insect herbivory provide an important mechanism responsible for positive effects on other insect herbivores
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