267 research outputs found
Non-saturating large magnetoresistance in semimetals
The rapidly expanding class of quantum materials known as {\emph{topological
semimetals}} (TSM) display unique transport properties, including a striking
dependence of resistivity on applied magnetic field, that are of great interest
for both scientific and technological reasons. However, experimental signatures
that can identify or discern the dominant mechanism and connect to available
theories are scarce. Here we present the magnetic susceptibility (), the
tangent of the Hall angle () along with magnetoresistance in four
different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb and
TaSb, all of which exhibit non-saturating large MR. We find that the
distinctly different temperature dependences, and the values of
in phosphides and antimonates serve as empirical criteria to
sort the MR from different origins: NbP and TaP being uncompensated semimetals
with linear dispersion, in which the non-saturating magnetoresistance arises
due to guiding center motion, while NbSb and TaSb being {\it
compensated} semimetals, with a magnetoresistance emerging from nearly perfect
charge compensation of two quadratic bands. Our results illustrate how a
combination of magnetotransport and susceptibility measurements may be used to
categorize the increasingly ubiquitous non-saturating large magnetoresistance
in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions,
6 figure
The Influence of Health Beliefs, of Resources, of Vaccination History, and of Health Anxiety on Intention to Accept COVID-19 Vaccination
Lattice Distortion and Magnetism of 3d- Perovskite Oxides
Several puzzling aspects of interplay of the experimental lattice distortion
and the the magnetic properties of four narrow -band perovskite oxides
(YTiO, LaTiO, YVO, and LaVO) are clarified using results of
first-principles electronic structure calculations. First, we derive parameters
of the effective Hubbard-type Hamiltonian for the isolated bands using
newly developed downfolding method for the kinetic-energy part and a hybrid
approach, based on the combination of the random-phase approximation and the
constraint local-density approximation, for the screened Coulomb interaction
part. Then, we solve the obtained Hamiltonian using a number of techniques,
including the mean-field Hartree-Fock (HF) approximation, the second-order
perturbation theory for the correlation energy, and a variational superexchange
theory. Even though the crystal-field splitting is not particularly large to
quench the orbital degrees of freedom, the crystal distortion imposes a severe
constraint on the form of the possible orbital states, which favor the
formation of the experimentally observed magnetic structures in YTiO,
YVO_, and LaVO even at the HF level. Beyond the HF approximation, the
correlations effects systematically improve the agreement with the experimental
data. Using the same type of approximations we could not reproduce the correct
magnetic ground state of LaTiO. However, we expect that the situation may
change by systematically improving the level of approximations for dealing with
the correlation effects.Comment: 30 pages, 17 figures, 8 tables, high-quality figures are available
via e-mai
A Quantum Monte Carlo algorithm for non-local corrections to the Dynamical Mean-Field Approximation
We present the algorithmic details of the dynamical cluster approximation
(DCA), with a quantum Monte Carlo (QMC) method used to solve the effective
cluster problem. The DCA is a fully-causal approach which systematically
restores non-local correlations to the dynamical mean field approximation
(DMFA) while preserving the lattice symmetries. The DCA becomes exact for an
infinite cluster size, while reducing to the DMFA for a cluster size of unity.
We present a generalization of the Hirsch-Fye QMC algorithm for the solution of
the embedded cluster problem. We use the two-dimensional Hubbard model to
illustrate the performance of the DCA technique. At half-filling, we show that
the DCA drives the spurious finite-temperature antiferromagnetic transition
found in the DMFA slowly towards zero temperature as the cluster size
increases, in conformity with the Mermin-Wagner theorem. Moreover, we find that
there is a finite temperature metal to insulator transition which persists into
the weak-coupling regime. This suggests that the magnetism of the model is
Heisenberg like for all non-zero interactions. Away from half-filling, we find
that the sign problem that arises in QMC simulations is significantly less
severe in the context of DCA. Hence, we were able to obtain good statistics for
small clusters. For these clusters, the DCA results show evidence of non-Fermi
liquid behavior and superconductivity near half-filling.Comment: 25 pages, 15 figure
The Pervasive Effects of ER Stress on a Typical Endocrine Cell: Dedifferentiation, Mesenchymal Shift and Antioxidant Response in the Thyrocyte
none13noThe endoplasmic reticulum stress and the unfolded protein response are triggered following an imbalance between protein load and protein folding. Until recently, two possible outcomes of the unfolded protein response have been considered: life or death. We sought to substantiate a third alternative, dedifferentiation, mesenchymal shift, and activation of the antioxidant response by using typical endocrine cells, i.e. thyroid cells. The thyroid is a unique system both of endoplasmic reticulum stress (a single protein, thyroglobulin represents the majority of proteins synthesized in the endoplasmic reticulum by the thyrocyte) and of polarized epithelium (the single layer of thyrocytes delimiting the follicle). Following endoplasmic reticulum stress, in thyroid cells the folding of thyroglobulin was disrupted. The mRNAs of unfolded protein response were induced or spliced (X-box binding protein-1). Differentiation was inhibited: mRNA levels of thyroid specific genes, and of thyroid transcription factors were dramatically downregulated, at least in part, transcriptionally. The dedifferentiating response was accompanied by an upregulation of mRNAs of antioxidant genes. Moreover, cadherin-1, and the thyroid (and kidney)-specific cadherin-16 mRNAs were downregulated, vimentin, and SNAI1 mRNAs were upregulated. In addition, loss of cortical actin and stress fibers formation were observed. Together, these data indicate that ER stress in thyroid cells induces dedifferentiation, loss of epithelial organization, shift towards a mesenchymal phenotype, and activation of the antioxidant response, highlighting, at the same time, a new and wide strategy to achieve survival following ER stress, and, as a sort of the other side of the coin, a possible new molecular mechanism of decline/loss of function leading to a deficit of thyroid hormones formation.openUlianich L.; Mirra P.; Garbi C.; Cali G.; Conza D.; Treglia A.S.; Miraglia A.; Punzi D.; Miele C.; Raciti G.A.; Beguinot F.; Consiglio E.; Di Jeso B.Ulianich, L.; Mirra, P.; Garbi, C.; Cali, G.; Conza, D.; Treglia, A. S.; Miraglia, A.; Punzi, D.; Miele, C.; Raciti, G. A.; Beguinot, F.; Consiglio, E.; Di Jeso, B
Evolution of spectral function in a doped Mott insulator : surface vs. bulk contributions
We study the evolution of the spectral function with progressive hole doping
in a Mott insulator, with = 0.0 - 0.5. The spectral
features indicate a bulk-to-surface metal-insulator transition in this system.
Doping dependent changes in the bulk electronic structure are shown to be
incompatible with existing theoretical predictions. An empirical description
based on the single parameter, , is shown to describe consistently the
spectral evolution.Comment: Revtex, 4 pages, 3 postscript figures. To appear in Phys. Rev. Let
How Photogenerated I<sub>2</sub> Induces I-Rich Phase Formation in Lead Mixed Halide Perovskites
Bandgap tunability of lead mixed halide perovskites (LMHPs) is a crucial characteristic for versatile optoelectronic applications. Nevertheless, LMHPs show the formation of iodide-rich (I-rich) phase under illumination, which destabilizes the semiconductor bandgap and impedes their exploitation. Here, it is shown that how I2, photogenerated upon charge carrier trapping at iodine interstitials in LMHPs, can promote the formation of I-rich phase. I2 can react with bromide (Br−) in the perovskite to form a trihalide ion I2Br− (Iδ−-Iδ+-Brδ−), whose negatively charged iodide (Iδ−) can further exchange with another lattice Br− to form the I-rich phase. Importantly, it is observed that the effectiveness of the process is dependent on the overall stability of the crystalline perovskite structure. Therefore, the bandgap instability in LMHPs is governed by two factors, i.e., the density of native defects leading to I2 production and the Br− binding strength within the crystalline unit. Eventually, this study provides rules for the design of chemical composition in LMHPs to reach their full potential for optoelectronic devices.</p
How Photogenerated I2 Induces I-Rich Phase Formation in Lead Mixed Halide Perovskites
Bandgap tunability of lead mixed halide perovskites (LMHPs) is a crucial characteristic for versatile optoelectronic applications. Nevertheless, LMHPs show the formation of iodide-rich (I-rich) phase under illumination, which destabilizes the semiconductor bandgap and impedes their exploitation. Here, it is shown that how I2 , photogenerated upon charge carrier trapping at iodine interstitials in LMHPs, can promote the formation of I-rich phase. I2 can react with bromide (Br- ) in the perovskite to form a trihalide ion I2 Br- (Iδ- -Iδ+ -Brδ- ), whose negatively charged iodide (Iδ- ) can further exchange with another lattice Br- to form the I-rich phase. Importantly, it is observed that the effectiveness of the process is dependent on the overall stability of the crystalline perovskite structure. Therefore, the bandgap instability in LMHPs is governed by two factors, i.e., the density of native defects leading to I2 production and the Br- binding strength within the crystalline unit. Eventually, this study provides rules for the design of chemical composition in LMHPs to reach their full potential for optoelectronic devices
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