189 research outputs found
Near room-temperature colossal magnetodielectricity and multiglass properties in partially-disordered La2NiMnO6
We report magnetic, dielectric and magnetodielectric responses of pure
monoclinic bulk phase of partially-disordered La2NiMnO6, exhibiting a spectrum
of unusual properties and establish that this system intrinsically is a true
multiglass with a large magnetodielectric coupling (8-20%) over a wide range of
temperatures (150 - 300 K). Specifically, our results establish a unique way to
obtain colossal magnetodielectricity, independent of any striction effects, by
engineering the asymmetric hopping contribution to the dielectric constant via
the tuning of the relative spin orientations between neighboring magnetic ions
in a transition metal oxide system. We discuss the role of anti-site (Ni-Mn)
disorder in emergence of these unusual properties.Comment: 5 pages, 4 figures, Slightly revised version of previous article in
condmat: arXiv:1202.4319v
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Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide : Experiment and Theory
The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS2) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around Pc, we observe a superconducting dome with a maximum superconducting transition temperature Tc=9.1 K. First-principles calculations of the electronic structure predict that, under ambient conditions, the undistorted structure is characterized by a phonon instability at finite momentum close to the experimental CDW wave vector. Upon compression, this instability is found to disappear, indicating the suppression of CDW order. The calculations reveal an electronic topological transition (ETT), which occurs before the suppression of the phonon instability, suggesting that the ETT alone is not directly causing the structural change in the system. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods. While a d wave and single-gap BCS prediction cannot describe the lower critical field Hc1 data, the temperature dependence of the Hc1 can be well described by a single-gap anisotropic s-wave order parameter. © 2020 authors. Published by the American Physical Society
High photon energy spectroscopy of NiO: experiment and theory
We have revisited the valence band electronic structure of NiO by means of
hard x-ray photoemission spectroscopy (HAXPES) together with theoretical
calculations using both the GW method and the local density approximation +
dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity
problem in DMFT is solved through the exact diagonalization (ED) method. We
show that the LDA+DMFT method alone cannot explain all the observed structures
in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and
p derived states to properly position their binding energies. Our results
establish that a combination of the GW and DMFT methods is necessary for
correctly describing the electronic structure of NiO in a proper ab-initio
framework. We also demonstrate that the inclusion of photoionization cross
section is crucial to interpret the HAXPES spectra of NiO.We argue that our
conclusions are general and that the here suggested approach is appropriate for
any complex transition metal oxide.Comment: 16 pages, 5 figure
Enforced expression of GATA-3 during T cell development inhibits maturation of CD8 single-positive cells and induces thymic lymphoma in transgenic mice
The zinc finger transcription factor GATA-3 is of critical importance for
early T cell development and commitment of Th2 cells. To study the role of
GATA-3 in early T cell development, we analyzed and modified GATA-3
expression in vivo. In mice carrying a targeted insertion of a lacZ
reporter on one allele, we found that GATA-3 transcription in CD4(+)CD8(+)
double-positive thymocytes correlated with the onset of positive selection
events, i.e., TCRalphabeta up-regulation and CD69 expression. LacZ
expression remained high ( approximately 80% of cells) during maturation
of CD4 single-positive (SP) cells in the thymus, but in developing CD8 SP
cells the fraction of lacZ-expressing cells decreased to <20%. We modified
this pattern by enforced GATA-3 expression driven by the CD2 locus control
region, which provides transcription of GATA-3 throughout T cell
development. In two independent CD2-GATA3-transgenic lines, approximately
50% of the mice developed thymic lymphoblastoid tumors that were
CD4(+)CD8(+/low) and mostly CD3(+). In tumor-free CD2-GATA3-transgenic
mice, the total numbers of CD8 SP cells in the thymus were within normal
ranges, but their maturation was hampered, as indicated by increased
apoptosis of CD8 SP cells and a selective deficiency of mature
CD69(low)HSA(low) CD8 SP cells. In the spleen and lymph nodes, the numbers
of CD8(+) T cells were significantly reduced. These findings indicate that
GATA-3 supports development of the CD4 lineage and inhibits maturation of
CD8 SP cells in the thymus
Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn
Combining experiments with first principles calculations, we show that
site-specific doping of Mn into SrTiO3 has a decisive influence on the
dielectric properties of these doped systems. We find that phonon contributions
to the dielectric constant invariably decrease sharply on doping at any site.
However, a sizable, random dipolar contribution only for Mn at the Sr site
arises from a strong off-centric displacement of Mn in spite of Mn being in a
non-d0 state; this leads to a large dielectric constant at higher temperatures
and gives rise to a relaxor ferroelectric behavior at lower temperatures. We
also investigate magnetic properties in detail and critically reevaluate the
possibility of a true multi-glass state in such systems.Comment: 24 Pages, 2 Tables, 9 Figure
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