1,732 research outputs found
Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations
Recent experiments in iron pnictide superconductors reveal that, as the
putative magnetic quantum critical point is approached, different types of
magnetic order coexist over a narrow region of the phase diagram. Although
these magnetic configurations share the same wave-vectors, they break distinct
symmetries of the lattice. Importantly, the highest superconducting transition
temperature takes place close to this proliferation of near-degenerate magnetic
states. In this paper, we employ a renormalization group calculation to show
that such a behavior naturally arises due to the effects of spin-orbit coupling
on the quantum magnetic fluctuations. Formally, the enhanced magnetic
degeneracy near the quantum critical point is manifested as a stable Gaussian
fixed point with a large basin of attraction. Implications of our findings to
the superconductivity of the iron pnictides are also discussed.Comment: 6 pages, 2 figures, published versio
Magnetic phase diagram of the iron pnictides in the presence of spin-orbit coupling: Frustration between and magnetic phases
We investigate the impact of spin anisotropic interactions, promoted by
spin-orbit coupling, on the magnetic phase diagram of the iron-based
superconductors. Three distinct magnetic phases with Bragg peaks at
and are possible in these systems: one (i.e. orthorhombic)
symmetric stripe magnetic phase and two (i.e. tetragonal) symmetric
magnetic phases. While the spin anisotropic interactions allow the magnetic
moments to point in any direction in the phase, they restrict the
possible moment orientations in the phases. As a result, an interesting
scenario arises in which the spin anisotropic interactions favor a phase,
but the other spin isotropic interactions favor a phase. We study this
frustration via both mean-field and renormalization-group approaches. We find
that, to lift this frustration, a rich magnetic landscape emerges well below
the magnetic transition temperature, with novel , , and mixed
- phases. Near the putative magnetic quantum critical point, spin
anisotropies promote a stable Gaussian fixed point in the renormalization-group
flow, which is absent in the spin isotropic case, and is associated with a
near-degeneracy between and phases. We argue that this frustration
is the reason why most phases in the iron pnictides only appear inside
the phase, and discuss additional manifestations of this frustration in
the phase diagrams of these materials.Comment: 21 pages, 19 figures, published versio
Role of multiorbital effects in the magnetic phase diagram of iron-pnictides
We elucidate the pivotal role of the bandstructure's orbital content in
deciding the type of commensurate magnetic order stabilized within the
itinerant scenario of iron-pnictides. Recent experimental findings in the
tetragonal magnetic phase attest to the existence of the so-called charge and
spin ordered density wave over the spin-vortex crystal phase, the latter of
which tends to be favored in simplified band models of itinerant magnetism.
Here we show that employing a multiorbital itinerant Landau approach based on
realistic bandstructures can account for the experimentally observed magnetic
phase, and thus shed light on the importance of the orbital content in deciding
the magnetic order. In addition, we remark that the presence of a hole pocket
centered at the Brillouin zone's -point favors a magnetic stripe
rather than a tetragonal magnetic phase. For inferring the symmetry properties
of the different magnetic phases, we formulate our theory in terms of magnetic
order parameters transforming according to irreducible representations of the
ensuing D point group. The latter method not only provides
transparent understanding of the symmetry breaking schemes but also reveals
that the leading instabilities always belong to the subset
of irreducible representations, independent of their C or C nature.Comment: 11 pages, 6 figure
A Handbook for New Actors in Space: A Community Resource for the Sustainable Development of Space
Virtual environments for telerobotic shared control
The use of a virtual environment to bring about telerobotic shared control is discussed. A knowledge base, referred to as the World Model, is used to aid the system in its decision making. Information from the World Model is displayed visually in order to aid the human side of human-computer interface
Structure, function and nutritional potential of milk osteopontin
AbstractOsteopontin (OPN) is a multifunctional protein present in most tissues and body fluids, with the highest concentrations found in milk. Processes for isolation of OPN from bovine milk for use in infant formula have been developed and studies have investigated the effects of oral administration of milk OPN. At the same time, plasma OPN levels have been shown to be elevated in some types of cancer, and OPN has been suggested as a potential diagnostic marker for cancer. OPN exists in several different isoforms in vivo, of which presumably only a minority is directly or indirectly implicated in cancer related events. In this article, we review the differences between milk-derived OPN and OPN derived from transformed cells and compare the structure of OPN from human and bovine milk. Furthermore, current knowledge about the function of OPN in milk and recent findings about the effect of orally presented OPN is discussed
Facile synthesis of <em>o</em>-Nitrobenzyl carbamate and 1-(2-Nitrophenylethyl) carbamate Protected <em>α,w</em>-Diamines
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