138 research outputs found
Probing spin correlations using angle-resolved photoemission in a coupled metallic/Mott insulator system
Funding: European Research Council (Grant Nos. ERC-714193-QUESTDO and ERC-319286-QMAC), the Royal Society, the Leverhulme Trust (Grant Nos. RL-2016-006 and PLP-2015-144R); EPSRC for PhD studentship support through grant numbers EP/L015110/1 and EP/K503162/1. I.M. acknowledges PhD studentship support from the IMPRS for the Chemistry and Physics of Quantum MaterialsA nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO2, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an “intertwined” excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO2 as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials.Publisher PDFPeer reviewe
Specific Heat Discontinuity, deltaC, at Tc in BaFe2(As0.7P0.3)2 - Consistent with Unconventional Superconductivity
We report the specific heat discontinuity, deltaC/Tc, at Tc = 28.2 K of a
collage of single crystals of BaFe2(As0.7P0.3)2 and compare the measured value
of 38.5 mJ/molK**2 with other iron pnictide and iron chalcogenide (FePn/Ch)
superconductors. This value agrees well with the trend established by Bud'ko,
Ni and Canfield who found that deltaC/Tc ~ a*Tc**2 for 14 examples of doped
Ba1-xKxFe2As2 and BaFe2-xTMxAs2, where the transition metal TM=Co and Ni. We
extend their analysis to include all the FePn/Ch superconductors for which
deltaC/Tc is currently known and find deltaC/Tc ~ a*Tc**1.9 and a=0.083
mJ/molK**4. A comparison with the elemental superconductors with Tc>1 K and
with A-15 superconductors shows that, contrary to the FePn/Ch superconductors,
electron-phonon-coupled conventional superconductors exhibit a significantly
different dependence of deltaC on Tc, namely deltaC/Tc ~ Tc**0.9. However
deltaC/gamma*Tc appears to be comparable in all three classes (FePn/Ch,
elemental and A-15) of superconductors with, e. g., deltaC/gamma*Tc=2.4 for
BaFe2(As0.7P0.3)2. A discussion of the possible implications of these
phenomenological comparisons for the unconventional superconductivity believed
to exist in the FePn/Ch is given.Comment: some disagreement in reference and footnote numbering with the
published versio
Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding
Within the broad class of multiferroics (compounds showing a coexistence of
magnetism and ferroelectricity), we focus on the subclass of "improper
electronic ferroelectrics", i.e. correlated materials where electronic degrees
of freedom (such as spin, charge or orbital) drive ferroelectricity. In
particular, in spin-induced ferroelectrics, there is not only a {\em
coexistence} of the two intriguing magnetic and dipolar orders; rather, there
is such an intimate link that one drives the other, suggesting a giant
magnetoelectric coupling. Via first-principles approaches based on density
functional theory, we review the microscopic mechanisms at the basis of
multiferroicity in several compounds, ranging from transition metal oxides to
organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic
frameworks, MOFs)Comment: 22 pages, 9 figure
Kazališni fragment II
Engineering and enhancing inversion symmetry breaking in solids is a major
goal in condensed matter physics and materials science, as a route to advancing
new physics and applications ranging from improved ferroelectrics for memory
devices to materials hosting Majorana zero modes for quantum computing. Here,
we uncover a new mechanism for realising a much larger energy scale of
inversion symmetry breaking at surfaces and interfaces than is typically
achieved. The key ingredient is a pronounced asymmetry of surface hopping
energies, i.e. a kinetic energy-driven inversion symmetry breaking, whose
energy scale is pinned at a significant fraction of the bandwidth. We show,
from spin- and angle-resolved photoemission, how this enables surface states of
3d and 4d-based transition-metal oxides to surprisingly develop some of the
largest Rashba-like spin splittings that are known. Our findings open new
possibilities to produce spin textured states in oxides which exploit the full
potential of the bare atomic spin-orbit coupling, raising exciting prospects
for oxide spintronics. More generally, the core structural building blocks
which enable this are common to numerous materials, providing the prospect of
enhanced inversion symmetry breaking at judiciously-chosen surfaces of a
plethora of compounds, and suggesting routes to interfacial control of
inversion symmetry breaking in designer heterostructures
The MAGPI Survey -- science goals, design, observing strategy, early results and theoretical framework
© The Author(s), 2021. Published by Cambridge University Press on behalf of the Astronomical Society of Australia. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1017/pasa.2021.25We present an overview of the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, a Large Program on ESO/VLT. MAGPI is designed to study the physical drivers of galaxy transformation at a lookback time of 3-4 Gyr, during which the dynamical, morphological, and chemical properties of galaxies are predicted to evolve significantly. The survey uses new medium-deep adaptive optics aided MUSE observations of fields selected from the GAMA survey, providing a wealth of publicly available ancillary multi-wavelength data. With these data, MAGPI will map the kinematic and chemical properties of stars and ionised gas for a sample of 60 massive (> 7 x 10^10 M_Sun) central galaxies at 0.25 < zPeer reviewe
Universal behavior of the upper critical field in iron based superconductors
The newly discovered iron-based high temperature superconductors have
demonstrated rich physical properties. Here we give a brief review on the
recent studies of the upper critical field and its anisotropy in a few typical
series of the iron-based superconductors (FeSCs). In spite of their characters
of a layered crystal structure, all the FeSCs possess an extremely large upper
critical field and a weak anisotropy of superconductivity, being unique among
the layered superconductors. These particular properties indicate potential
applications of the FeSCs in the future. Based on the experimental facts of the
FeSCs, we will discuss the possible mechanisms of pair breaking in high
magnetic fields and its restrictions on the theoretical analysis of the
superconducting pairing mechanisms.Comment: 24 pages, 10 figure
Spatial clustering and risk factors of malaria infections in Ratanakiri Province, Cambodia
Background: Malaria incidence worldwide has steadily declined over the past decades. Consequently, increasingly more countries will proceed from control to elimination. The malaria distribution in low incidence settings appears patchy, and local transmission hotspots are a continuous source of infection. In this study, species-specific clusters and associated risk factors were identified based on malaria prevalence data collected in the north-east of Cambodia. In addition, Plasmodium falciparum genetic diversity, population structure and gene flows were studied.Method: In 2012, blood samples from 5793 randomly selected individuals living in 117 villages were collected from Ratanakiri province, Cambodia. Malariometric data of each participant were simultaneously accumulated using a standard questionnaire. A two-step PCR allowed for species-specific detection of malaria parasites, and SNPgenotyping of P. falciparum was performed. SaTScan was used to determine species-specific areas of elevated risk to infection, and univariate and multivariate risk analyses were carried out.Result: PCR diagnosis found 368 positive individuals (6.4%) for malaria parasites, of which 22% contained mixed species infections. The occurrence of these co-infections was more frequent than expected. Specific areas with elevated risk of infection were detected for all Plasmodium species. The clusters for Falciparum, Vivax and Ovale malaria appeared in the north of the province along the main river, while the cluster for Malariae malaria was situated elsewhere. The relative risk to be a malaria parasite carrier within clusters along the river was twice that outside the area. The main risk factor associated with three out of four malaria species was overnight stay in the plot hut, a human behaviour associated with indigenous farming. Haplotypes did not show clear geographical population structure, but pairwise Fst value comparison indicated higher parasite flow along the river.Discussion: Spatial aggregation of malaria parasite carriers, and the identification of malaria species-specific risk factors provide key insights in malaria epidemiology in low transmission settings, which can guide targeted supplementary interventions. Consequently, future malaria programmes in the province should implement additional specific policies targeting households staying overnight at their farms outside the village, in addition to migrants and forest workers
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