562 research outputs found
Pairing interactions and pairing mechanism in high temperature copper oxide superconductors
The polaron binding energy E_{p} in undoped parent cuprates has been
determined to be about 1.0 eV from the unconventional oxygen-isotope effect on
the antiferromagnetic ordering temperature. The deduced value of E_{p} is in
quantitative agreement with that estimated from independent optical data and
that estimated theoretically from the measured dielectric constants. The
substantial oxygen-isotope effect on the in-plane supercarrier mass observed in
optimally doped cuprates suggests that polarons are bound into the Cooper
pairs. We also identify the phonon modes that are strongly coupled to
conduction electrons from the angle-resolved photoemission spectroscopy,
tunneling spectra, and optical data. We consistently show that there is a very
strong electron-phonon coupling feature at a phonon energy of about 20 meV
along the antinodal direction and that this coupling becomes weaker towards the
diagonal direction. We further show that high-temperature superconductivity in
cuprates is caused by strong electron-phonon coupling, polaronic effect, and
significant coupling with 2 eV Cu-O charge transfer fluctuation.Comment: 11 pages, 7 figure
Structure of the exotic spin-flop states in BaCu2Si2O7
The unusual 2-stage spin flop transition in BaCu2Si2O7 is studied by
single-crystal neutron diffraction. The magnetic structures of the various
spin-flop phases are determined. The results appear to be inconsistent with the
previously proposed theoretical explanation of the 2-stage transition.Comment: 6 pages 5 figure
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
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Sex Hormone-Binding Globulin Levels Are Inversely Associated With Nonalcoholic Fatty Liver Disease in HIV-Infected and -Uninfected Men.
BackgroundNonalcoholic fatty liver disease (NAFLD) is a leading cause of liver disease worldwide. Elevated sex hormone-binding globulin (SHBG) levels have been observed in the setting of HIV and may protect against some metabolic disorders. We aimed to investigate whether higher SHBG levels may protect against NAFLD in men with/without HIV.MethodsNAFLD was assessed using noncontrast computed tomography in 530 men in the Multicenter AIDS Cohort Study (MACS) who drank <3 alcoholic drinks/d and were uninfected with chronic hepatitis C or B (340HIV+, 190HIV-). Morning serum samples were tested for SHBG, total testosterone (TT), and adiponectin. Multivariable logistic regression was used to assess associations between HIV, SHBG, TT, adiponectin, and NAFLD.ResultsMedian SHBG was highest among HIV+/NAFLD- men and lowest among HIV-/NAFLD+ men. Adjusted for demographics, HIV, visceral adiposity, HOMA-IR, TT, and PNPLA3 genotype, higher SHBG was associated with lower odds of NAFLD (odds ratio [OR], 0.52 per doubling; 95% confidence interval [CI], 0.34-0.80). In separate multivariable models without SHBG, HIV (OR, 0.46; 95% CI, 0.26-0.79) and higher adiponectin (OR, 0.66 per doubling; 95% CI, 0.49-0.89) were associated with lower NAFLD odds, whereas TT was not significantly associated (OR, 0.74 per doubling; 95% CI, 0.53-1.04). Adjusting for SHBG attenuated the associations of HIV (OR, 0.61; 95% CI, 0.34-1.08) and adiponectin (OR, 0.74; 95% CI, 0.54-1.02) with NAFLD.ConclusionsSHBG levels were higher among HIV+ men, were independently associated with lower NAFLD, and could partially explain the associations of HIV and higher adiponectin with lower NAFLD in our cohort. These findings suggest that SHBG may protect against NAFLD, supporting further prospective and mechanistic studies
Properties and Detection of Spin Nematic Order in Strongly Correlated Electron Systems
A spin nematic is a state which breaks spin SU(2) symmetry while preserving
translational and time reversal symmetries. Spin nematic order can arise
naturally from charge fluctuations of a spin stripe state. Focusing on the
possible existence of such a state in strongly correlated electron systems, we
build a nematic wave function starting from a t-J type model. The nematic is a
spin-two operator, and therefore does not couple directly to neutrons. However,
we show that neutron scattering and Knight shift experiments can detect the
spin anisotropy of electrons moving in a nematic background. We find the mean
field phase diagram for the nematic taking into account spin-orbit effects.Comment: 13 pages, 11 figures. (v2) References adde
Theory of extraordinary optical transmission through subwavelength hole arrays
We present a fully three-dimensional theoretical study of the extraordinary
transmission of light through subwavelength hole arrays in optically thick
metal films. Good agreement is obtained with experimental data. An analytical
minimal model is also developed, which conclusively shows that the enhancement
of transmission is due to tunneling through surface plasmons formed on each
metal-dielectric interfaces. Different regimes of tunneling (resonant through a
''surface plasmon molecule", or sequential through two isolated surface
plasmons) are found depending on the geometrical parameters defining the
system.Comment: 4 pages, 4 figure
Dzyaloshinsky-Moriya antisymmetric exchange coupling in cuprates: Oxygen effects
We revisit a problem of Dzyaloshinsky-Moriya antisymmetric exchange coupling
for a single bond in cuprates specifying the local spin-orbital contributions
to Dzyaloshinsky vector focusing on the oxygen term. The Dzyaloshinsky vector
and respective weak ferromagnetic moment is shown to be a superposition of
comparable and, sometimes, competing local Cu and O contributions. The
intermediate oxygen O Knight shift is shown to be an effective tool to
inspect the effects of Dzyaloshinsky-Moriya coupling in an external magnetic
field. We predict the effect of oxygen weak antiferromagnetism in
edge-shared CuO chains due to uncompensated oxygen Dzyaloshinsky vectors.
Finally, we revisit the effects of symmetric spin anisotropy, in particular,
those directly induced by Dzyaloshinsky-Moriya coupling.Comment: 12 pages, 2 figures, submitted to JET
Suppression of Antiferromagnetic Order by Light Hole Doping in La_2Cu_{1-x}Li_xO_4: A ^{139}La NQR Study
^{139}La nuclear quadrupole resonance measurements in lightly doped
La_2Cu_{1-x}Li_xO_4 have been performed to reveal the dependence of the
magnetic properties of the antiferromagnetic CuO_2 planes on the character of
the doped holes and their interactions with the dopant. A detailed study shows
that the magnetic properties are remarkably insensitive to the character of the
dopant impurity. This indicates that the added holes form previously
unrecognized collective structures.Comment: 4 pages, 3 figures. Slightly modified version, as accepted for
publication in Physical Review Letter
Familial co-aggregation and shared genetics of cardiometabolic disorders and traits:data from the multi-generational Lifelines Cohort Study
BACKGROUND: It is unclear to what extent genetics explain the familial clustering and the co-occurrence of distinct cardiometabolic disorders in the general population. We therefore aimed to quantify the familial (co-)aggregation of various cardiometabolic disorders and to estimate the heritability of cardiometabolic traits and their genetic correlations using the large, multi-generational Lifelines Cohort Study.METHODS: We used baseline data of 162,416 participants from Lifelines. Cardiometabolic disorders including type 2 diabetes (T2D), cardiovascular diseases, hypertension, obesity, hypercholesterolemia, and metabolic syndrome (MetS), were defined in adult participants. Fifteen additional cardiometabolic traits indexing obesity, blood pressure, inflammation, glucose regulation, and lipid levels were measured in all included participants. Recurrence risk ratios (λ R) for first-degree relatives (FDR) indexed familial (co-)aggregation of cardiometabolic disorders using modified conditional Cox proportional hazards models and were compared to those of spouses. Heritability (h 2), shared environment, and genetic correlation (r g) were estimated using restricted maximum likelihood variance decomposition methods, adjusted for age, age 2, and sex. RESULTS: Individuals with a first-degree relative with a cardiometabolic disorder had a higher risk of the same disorder, ranging from λ FDR of 1.23 (95% CI 1.20-1.25) for hypertension to λ FDR of 2.48 (95% CI 2.15-2.86) for T2D. Most of these were higher than in spouses (λ Spouses < λ FDR), except for obesity which was slightly higher in spouses. We found moderate heritability for cardiometabolic traits (from h 2 CRP: 0.26 to h 2 HDL: 0.50). Cardiometabolic disorders showed positive familial co-aggregation, particularly between T2D, MetS, and obesity (from λ FDR obesity-MetS: 1.28 (95% CI 1.24-1.32) to λ FDR MetS-T2D: 1.61 (95% CI 1.52-1.70)), consistent with the genetic correlations between continuous intermediate traits (ranging from r g HDL-Triglycerides: - 0.53 to r g LDL-Apolipoprotein B: 0.94). CONCLUSIONS: There is positive familial (co-)aggregation of cardiometabolic disorder, moderate heritability of intermediate traits, and moderate genetic correlations between traits. These results indicate that shared genetics and common genetic architecture contribute to cardiometabolic disease.</p
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