2,741 research outputs found
Electronic inhomogeneity at magnetic domain walls in strongly-correlated systems
We show that nano-scale variations of the order parameter in
strongly-correlated systems can induce local spatial regions such as domain
walls that exhibit electronic properties representative of a different, but
nearby, part of the phase diagram. This is done by means of a Landau-Ginzburg
analysis of a metallic ferromagnetic system near an antiferromagnetic phase
boundary. The strong spin gradients at a wall between domains of different spin
orientation drive the formation of a new type of domain wall, where the central
core is an insulating antiferromagnet, and connects two metallic ferromagnetic
domains. We calculate the charge transport properties of this wall, and find
that its resistance is large enough to account for recent experimental results
in colossal magnetoresistance materials. The technological implications of this
finding for switchable magnetic media are discussed.Comment: Version submitted to Physical Review Letters, except for minor
revisions to reference
Reliable quantification of 1,2-dihydroxynaphthalene in urine using a conjugated reference compound for calibration.
After environmental and occupational exposure to naphthalene, 1,2-dihydroxynaphthalene (1,2-DHN) was shown to be one major metabolite in human naphthalene metabolism. However, the instability of free 1,2-DHN complicates the reliable determination of this promising biomarker in urine. To solve this stability problem, glucuronide conjugates of 1,2-DHN and the corresponding isotopically labelled D-6-1,2-dihydroxynaphthalene (D-6-1,2-DHN) were synthesised and applied as reference material and internal standard in a gas chromatographic-tandem mass spectrometric (GC-MS/MS) method. The determination of 1- and 2-naphthol (1-MHN, 2-MHN) was included in the procedure to enable a comprehensive assessment of naphthalene metabolism and exposure. The results of the validation showed a high reliability and sensitivity of the method. The detection limits range from 0.05 to 0.16 mu g/L. Precision and repeatability were determined to range from 1.4 to 6.6% for all parameters. The simultaneous determination of 1- and 2-MHN as additional parameters besides 1,2-DHN enables the application of the method for further metabolism and kinetic studies on naphthalene. The use of glucuronide-derivative reference substances and the application of structurally matched isotopic-labelled internal standards for each substance guarantee a reliable quantification of the main naphthalene metabolites 1,2-DHN and 1- and 2-MHN
Enhanced Efficiency of Light-Trapping Nanoantenna Arrays for Thin Film Solar Cells
We suggest a novel concept of efficient light-trapping structures for
thin-film solar cells based on arrays of planar nanoantennas operating far from
plasmonic resonances. The operation principle of our structures relies on the
excitation of chessboard-like collective modes of the nanoantenna arrays with
the field localized between the neighboring metal elements. We demonstrated
theoretically substantial enhancement of solar-cell short-circuit current by
the designed light-trapping structure in the whole spectrum range of the
solar-cell operation compared to conventional structures employing
anti-reflecting coating. Our approach provides a general background for a
design of different types of efficient broadband light-trapping structures for
thin-film solar-cell technologically compatible with large-area thin-film
fabrication techniques
Multicolour fluorescent "sulfide-sulfone" diarylethenes with high photo-fatigue resistance.
Compact "push-pull" photochromic diaryethenes (DAEs) with unsymmetric oxidation pattern of the benzothiophene core display multicolour fluorescence switching, as a result of dual emission from both "open" and "closed" forms. These DAEs also present an unprecedented photo-fatigue resistance
Quantum phase transition in the dioptase magnetic lattice
The study of quantum phase transitions, which are zero-temperature phase
transitions between distinct states of matter, is of current interest in
research since it allows for a description of low-temperature properties based
on universal relations. Here we show that the crystal green dioptase
Cu_6Si_6O_18 . 6H_2O, known to the ancient Roman as the gem of Venus, has a
magnetic crystal structure, formed by the Cu(II) ions, which allows for a
quantum phase transition between an antiferromagnetically ordered state and a
quantum spin liquid.Comment: 6 pages, 5 figures, EPL, in pres
About low field memory and negative magnetization in semiconductors and polymers
Ginzburg-Landau bulk magnetization of itinerant electrons can provide a
negative effective field in the Weiss model by coupling to localized magnetic
moments. The coupling enforces remnant magnetization, which can be negative or
positive depending on the sample magnetic history. Stable magnetic
susceptibility of coupled nonequilibrium subsystems with magnetization reversal
is always positive. Gauss-scale fields could be expected for switching between
negative and positive remnant moments in semiconductors with coupling at
ambient temperatures. Negative magnetization in ultra-high conducting polymers
is also discussed within the developed framework.Comment: 8 pages, no figure
Temperature evolution of magnetic structure of HoFeO by single crystal neutron diffraction
We have investigated the temperature evolution of the magnetic structures of
HoFeO by single crystal neutron diffraction. The three different magnetic
structures found as a function of temperature for \hfo\ are described by the
magnetic groups Pbn, Pbn and Pbn and are stable in the
temperature ranges 600-55~K, 55-37~K and 35~K respectively. In
all three the fundamental coupling between the Fe sub-lattices remains the same
and only their orientation and the degree of canting away from the ideal axial
direction varies. The magnetic polarisation of the Ho sub-lattices in these two
higher temperature regions, in which the major components of the Fe moment lie
along and , is very small. The canting of the moments from the axial
directions is attributed to the antisymmetric interactions allowed by the
crystal symmetry. They include contributions from single ion anisotropy as well
as the Dzyaloshinski antisymmetric exchange. In the low temperature phase two
further structural transitions are apparent in which the spontaneous
magnetisation changes sign with respect to the underlying antiferromagnetic
configuration. In this temperature range the antisymmetric exchange energy
varies rapidly as the the Ho sub-lattices begin to order. So long as the
ordered Ho moments are small the antisymmetric exchange is due only to Fe-Fe
interactions, but as the degree of Ho order increases the Fe-Ho interactions
take over whilst at the lowest temperatures, when the Ho moments approach
saturation the Ho-Ho interactions dominate. The reversals of the spontaneous
magnetisation found in this study suggest that in \hfo\ the sums of the Fe-Fe
and Ho-Ho antisymmetric interactions have the same sign as one another, but
that of the Ho-Fe terms is opposite
Endomorphisms of quantized Weyl algebras
Belov-Kanel and Kontsevich conjectured that the group of automorphisms of the
n'th Weyl algebra and the group of polynomial symplectomorphisms of C^2 are
canonically isomorphic. We discuss how this conjecture can be approached by
means of (second) quantized Weyl algebras at roots of unity
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