Hybridization of Bogoliubov Quasiparticles between Adjacent CuO_{2} Layers in the Triple-Layer Cuprate Bi_{2}Sr_{2}Ca_{2}Cu_{3}O_{10+δ} Studied by Angle-Resolved Photoemission Spectroscopy.

Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO_{2} layers in the triple-layer cuprate high-temperature superconductor Bi_{2}Sr_{2}Cu_{2}Cu_{3}O_{10+δ} is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anticrossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the d-wave superconducting gap of both BQP bands smoothly develops with momentum without an abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off nodal to the antinodal region, which is explained by the momentum dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs as well as the combination of phonon modes of the triple CuO_{2} layers and spin fluctuations represented by a four-well model are discussed.

Electronic Structure of Ce-Doped and -Undoped Nd_{2}CuO_{4} Superconducting Thin Films Studied by Hard X-Ray Photoemission and Soft X-Ray Absorption Spectroscopy.

In order to realize superconductivity in cuprates with the T^{'}-type structure, not only chemical substitution (Ce doping) but also postgrowth reduction annealing is necessary. In the case of thin films, however, well-designed reduction annealing alone without Ce doping can induce superconductivity in the T^{'}-type cuprates. In order to unveil the origin of superconductivity in the Ce-undoped T^{'}-type cuprates, we have performed bulk-sensitive hard x-ray photoemission and soft x-ray absorption spectroscopy on superconducting and nonsuperconducting Nd_{2-x}Ce_{x}CuO_{4} (x=0, 0.15, and 0.19) thin films. By postgrowth annealing, core-level spectra exhibited dramatic changes, which we attributed to the enhancement of core-hole screening in the CuO_{2} plane and the shift of chemical potential along with changes in the band filling. The result suggests that the superconducting Nd_{2}CuO_{4} film is doped with electrons despite the absence of the Ce substitution.

Stability of the Zhang-Rice Singlet with Doping in Lanthanum Strontium Copper Oxide Across the Superconducting Dome and Above.

The spin character of the states at the top of the valence band in doped La(2-x)Sr(x)CuO(4) (x=0.03, 0.07, 0.15, 0.22, and 0.30) has been investigated using spin-polarized resonant photoemission. A clear Zhang-Rice singlet (ZRS) is observed at all doping levels. Its stability and polarization are preserved as a function of doping, suggesting that the concept of the ZRS can be used across a wide doping range and up to the metallic nonsuperconducting overdoped regime. The results are significant for theoretical models that use the ZRS approximation and for the understanding of the peculiar interplay between the ZRS and the remaining localized spins.

Electronic excitations of a magnetic impurity state in the diluted magnetic semiconductor (Ga,Mn)As.

The electronic structure of doped Mn in (Ga,Mn)As is studied by resonant inelastic x-ray scattering. From configuration-interaction cluster-model calculations, the line shapes of the Mn L3 resonant inelastic x-ray scattering spectra can be explained by d-d excitations from the Mn ground state dominated by charge-transferred states, in which hole carriers are bound to the Mn impurities, rather than a pure acceptor Mn2+ ground state. Unlike archetypical d-d excitation, the peak widths are broader than the experimental energy resolution. We attribute the broadening to a finite lifetime of the d-d excitations, which decay rapidly to electron-hole pairs in the host valence and conduction bands through the hybridization of the Mn 3d orbital with the ligand band.

Dependence of carrier doping on the impurity potential in transition-metal-substituted FeAs-based superconductors.

In order to examine to what extent the rigid-band-like electron doping scenario is applicable to the transition metal-substituted Fe-based superconductors, we have performed angle-resolved photoemission spectroscopy studies of Ba(Fe(1-x)Ni(x))(2)As(2) (Ni-122) and Ba(Fe(1-x)Cu(x))(2)As(2) (Cu-122), and compared the results with Ba(Fe(1-x)Co(x))(2)As(2) (Co-122). We find that Ni 3d-derived features are formed below the Fe 3d band and that Cu 3d-derived ones further below it. The electron and hole Fermi surface (FS) volumes are found to increase and decrease with substitution, respectively, qualitatively consistent with the rigid-band model. However, the total extra electron number estimated from the FS volumes (the total electron FS volume minus the total hole FS volume) is found to decrease in going from Co-, Ni-, to Cu-122 for a fixed nominal extra electron number, that is, the number of electrons that participate in the formation of FS decreases with increasing impurity potential. We find that the Néel temperature T(N) and the critical temperature T(c) maximum are determined by the FS volumes rather than the nominal extra electron concentration or the substituted atom concentration.

Spectroscopic investigations of fungal biomarkers after exposure to heavy ion irradiation.

The main objective of the ongoing and future space exploration missions is the search for traces of extant or extinct life (biomarkers) on Mars. One of the main limiting factors on the survival of Earth-like life is the presence of harmful space radiation, that could damage or modify also biomolecules, therefore understanding the effects of radiation on terrestrial biomolecules stability and detectability is of utmost importance. Which terrestrial molecules could be preserved in a Martian radiation scenario? Here, we investigated the potential endurance of fungal biomolecules, by exposing de-hydrated colonies of the Antarctic cryptoendolithic black fungus Cryomyces antarcticus mixed with Antarctic sandstone and with two Martian regolith analogues to increasing doses (0, 250 and 1000 Gy) of accelerated ions, namely iron (Fe), argon (Ar) and helium (He) ions. We analyzed the feasibility to detect fungal compounds with Raman and Infrared spectroscopies after exposure to these space-relevant radiations.

Self-energy on the low- to high-energy electronic structure of correlated metal SrVO3.

The correlated electronic structure of SrVO(3) has been investigated by angle-resolved photoemission spectroscopy using in situ prepared thin films. Pronounced features of band renormalization have been observed: a sharp kink ∼60 meV below the Fermi level (E(F)) and a broad so-called "high-energy kink" ∼0.3 eV below E(F) as in the high-T(c) cuprates, although SrVO(3) does not show magnetic fluctuations. We have deduced the self-energy in a wide energy range by applying the Kramers-Kronig relation to the observed spectra. The obtained self-energy clearly shows a large energy scale of ∼0.7 eV, which is attributed to electron-electron interaction and gives rise to the ∼0.3 eV kink in the band dispersion as well as the incoherent peak ∼1.5 eV below E(F). The present analysis enables us to obtain a consistent picture for both the incoherent spectra and the band renormalization.

Unconventional exciton evolution from the pseudogap to superconducting phases in cuprates.

Electron quasiparticles play a crucial role in simplifying the description of many-body physics in solids with surprising success. Conventional Landau's Fermi-liquid and quasiparticle theories for high-temperature superconducting cuprates have, however, received skepticism from various angles. A path-breaking framework of electron fractionalization has been established to replace the Fermi-liquid theory for systems that show the fractional quantum Hall effect and the Mott insulating phenomena; whether it captures the essential physics of the pseudogap and superconducting phases of cuprates is still an open issue. Here, we show that excitonic excitation of optimally doped Bi2Sr2CaCu2O8+δ with energy far above the superconducting-gap energy scale, about 1 eV or even higher, is unusually enhanced by the onset of superconductivity. Our finding proves the involvement of such high-energy excitons in superconductivity. Therefore, the observed enhancement in the spectral weight of excitons imposes a crucial constraint on theories for the pseudogap and superconducting mechanisms. A simple two-component fermion model which embodies electron fractionalization in the pseudogap state provides a possible mechanism of this enhancement, pointing toward a novel route for understanding the electronic structure of superconducting cuprates.

Two-Fermi-surface superconducting state and a nodal d-wave energy gap of the electron-doped Sm1.85Ce0.15CuO(4-δ) cuprate superconductor.

We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate Sm1.85Ce0.15CuO(4-δ). The data show the existence of a nodal hole-pocket Fermi surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferrmagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole pocket is compatible with a d-wave symmetry.

Two-dimensional and three-dimensional Fermi surfaces of superconducting BaFe2(As(1-x)P(x))2 and their nesting properties revealed by angle-resolved photoemission spectroscopy.

We have studied the three-dimensional shapes of the Fermi surfaces (FSs) of BaFe(2)(As(1-x)P(x))(2) (x=0.38), where superconductivity is induced by isovalent P substitution and by angle-resolved photoemission spectroscopy. Moderately strong electron mass enhancement has been identified for both the electron and hole FSs. Among two observed hole FSs, the nearly two-dimensional one shows good nesting with the outer two-dimensional electron FS, but its orbital character is different from the outer electron FS. The three-dimensional hole FS shows poor nesting with the electron FSs. The present results suggest that the three dimensionality and the difference in the orbital character weaken FS nesting while partial nesting among the outer electron FSs of d(xy) character and/or that within the three-dimensional hole FS becomes dominant, which may lead to the nodal superconductivity.

Dimensional-crossover-driven metal-insulator transition in SrVO3 ultrathin films.

We have investigated the changes occurring in the electronic structure of digitally controlled SrVO(3) ultrathin films across the metal-insulator transition (MIT) by the film thickness using in situ photoemission spectroscopy. With decreasing film thickness, a pseudogap is formed at E(F) through spectral weight transfer from the coherent part to the incoherent part. The pseudogap finally evolves into an energy gap that is indicative of the MIT in a SrVO(3) ultrathin film. The observed spectral behavior is reproduced by layer dynamical-mean-field-theory calculations, and it indicates that the observed MIT is caused by the reduction in the bandwidth due to the dimensional crossover.

Energy-dependent enhancement of the electron-coupling spectrum of the underdoped Bi2Sr2CaCu2O(8+δ) superconductor.

We have determined the electron-coupling spectrum of superconducting Bi2Sr2CaCu2O(8+δ) from high-resolution angle-resolved photoemission spectra by two deconvolution-free robust methods. As hole concentration decreases, the coupling spectral weight at low energies ≲15 meV shows a twofold and nearly band-independent enhancement, while that around ∼65 meV increases moderately, and that in ≳130 meV decreases leading to a crossover of dominant coupling excitation between them. Our results suggest the competition among multiple screening effects, and provide important clues to the source of sufficiently strong low-energy coupling, λ(LE)≈1, in an underdoped system.

Enhanced superconducting gaps in the trilayer high-temperature Bi2Sr2Ca2Cu3O(10+δ) cuprate superconductor.

We report the first observation of the multilayer band splitting in the optimally doped trilayer cuprate Bi2Sr2Ca2Cu3O(10+δ) (Bi2223) by angle-resolved photoemission spectroscopy. The observed energy bands and Fermi surfaces are originated from the outer and inner CuO2 planes (OP and IP). The OP band is overdoped with a large d-wave gap around the node of Δ0∼43 meV while the IP is underdoped with an even large gap of Δ0∼60 meV. These energy gaps are much larger than those for the same doping level of the double-layer cuprates, which leads to the large Tc in Bi2223. We propose possible origins of the large superconducting gaps for the OP and IP: (1) minimal influence of out-of-plane disorder and a proximity effect and (2) interlayer tunneling of Cooper pairs between the OP and IP.

Excellent performance of aromatic polyguanamines induced by multiple hydrogen bondable tetraazacalix[2]arene[2]-triazine ring in their main chain.

A series of poly(guanamine) (c-PG)s containing tetraazacalix[2]arene[2]-triazine (mPDA2CyC2) were successfully prepared by solution polycondensation of mPDA2CyC2 with various aromatic diamines in an aprotic organic solvent with a lithium chloride additive (5 wt%) at 150 °C for 6 hours. The number-average molecular weights (M n)s of these c-PG polymers reached up to 31 500, with a relatively broad molecular weight distribution (M w/M n) of 5.3. They showed good solubility in aprotic organic solvents, such as N-methylpyrrolidone and N,N-dimethylacetamide at a concentration of 2 mg mL-1. The glass transition temperatures (T g) of the c-PG polymers were in the range 359 °C-392 °C, approximately 160 °C higher than those of counterpart polymers (i.e., with no aza-calixarene-based PG (l-PG)). The coefficients of thermal expansion (CTEs) of the c-PG polymers were 29.7-48.1 ppm K-1 (at 100 °C-150 °C), much lower than those of l-PG samples, i.e., 59.1-85.1 ppm K-1. Transparent and almost colorless c-PG films were successfully prepared by a solution casting method, showing maximum tensile strength (σ S), modulus (E γ), and elongation at break (E b) values of 151 MPa, 6.3 GPa, and 4.4%, respectively, for the c-PG polymer from mPDA2CyC2 and 4,4'-oxydianiline monomers. The corresponding l-PG film exhibited σ S, E γ, and E b values of just 76 MPa, 5.4 GPa, and 1.6%, respectively. These outstanding thermal and mechanical properties of the c-PG polymers can be attributed to their multiple hydrogen bonding interaction between mPDA2CyC2 residues in the polymer backbone. This interaction was identified by infrared spectroscopy measurements at the broad absorption band around 3000-3400 cm-1.

Band-dependent superconducting gap in SrFe2(As0.65P0.35)2 studied by angle-resolved photoemission spectroscopy.

The isovalent-substituted iron pnictide compound SrFe2(As1-xPx)2 exhibits multiple evidence for nodal superconductivity via various experimental probes, such as the penetration depth, nuclear magnetic resonance and specific heat measurements. The direct identification of the nodal superconducting (SC) gap structure is challenging, partly because the presence of nodes is not protected by symmetry but instead caused by an accidental sign change of the order parameter, and also because of the three-dimensionality of the electronic structure. We have studied the SC gaps of SrFe2(As0.65P0.35)2 in three-dimensional momentum space by synchrotron and laser-based angle-resolved photoemission spectroscopy. The three hole Fermi surfaces (FSs) at the zone center have SC gaps with different magnitudes, whereas the SC gaps of the electron FSs at the zone corner are almost isotropic and kz-independent. As a possible nodal SC gap structure, we propose that the SC gap of the outer hole FS changes sign around the Z-X [(0, 0, 2π) - (π, π, 2π)] direction.

Identification of Genes Responding to Low-Dose Arsenite Using HiCEP.

ABSTRACT Chronic ingestion of arsenic in polluted food and water can cause various human disorders including skin and lung cancers. Sensitive biomarkers from human tissue/cells could help to prevent chronic intoxication with low-dose arsenite. Using High-Coverage Expression Profiling (HiCEP), an Amplified Fragment Length Polymorphism (AFLP)-based gene expression profiling technique, we analyzed the expression of approximately 11,000 genes in human lung fibroblasts (HFLIII) and compared the profiles between cells, treated and untreated with 1 muM sodium arsenite (NaAsO(2)). Hundreds of genes appeared upregulated and downregulated more than two-fold, 2 h after the treatment. Marked induction was found (>4.4-fold) in a few genes including HMOX1, INHBA, and ANKRD11. Induction of the HMOX1 was detected with a dose of arsenite at as low as 0.3 muM (0.04 ppm) and reached its maximum at 4 h after the treatment. The arsenite-induced HMOX1 expression was attenuated by the promoted glutathione (GSH) synthesis by N-acetyl-L-cysteine (NAC). However, it was not affected by pretreating the cells with general radical scavengers, consistent with the fact that ionizing radiation at either high-or low-doses has never induced HMOX1 in the same assay system. Thus, induction of HMOX1 gene is highly sensitive and also selective against arsenite in the cells. The present process could provide a useful strategy for exploring biomarkers that might help in assessing the known and unknown risks of any natural and artificial toxic reagents.

ARPES studies on new types of electron-doped cuprate superconductors.

For more than thirty years since the discovery of superconductivity in cuprates, it has been widely agreed that the superconductivity is realized by doping a charge-transfer insulator with charge carriers through chemical substitution. For electron-doped cuprates, however, the recent development of reduction annealing methods has enabled superconductivity for a very small amount of or even without chemical substitution. In this article, we review recent angle-resolved photoemission spectroscopy studies on the new types of electron-doped cuprates with particular emphasis on the effect of reduction annealing. The presented results provide us with renewed insight into the phase diagram and the nature of the pseudogap not only on the electron-doped side but also in the entire doping range including hole doping.

Low-calcium dialysate improves mineral metabolism in hemodialysis patients.

BACKGROUND: The Kidney Disease Outcomes Quality Initiative (K/DOQI) Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease recommend 1.25 mmol/l Ca dialysate for both hemodialysis and peritoneal dialysis, while 1.5 mmol/l Ca dialysate has been used in our dialysis center. METHODS: Therefore, we switched the dialysate calcium concentration from 1.5 - 1.25 mmol/l and observed the effects on serum calcium (S-Ca), phosphorus (S-P), 1-84 parathyroid hormone (whole PTH, w-PTH), bone-specific alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase isoform 5b (TRACP-5b) for 6 months in 58 hemodialysis patients. Prescription of active vitamin D (VD) metabolites and Ca carbonate was increased in response to the changes in laboratory data. RESULTS: Decrease of S-Ca was evident at 2 weeks and S-Ca remained low for 6 months. Transient elevation of S-P, which might be caused by stimulated bone resorption, was observed after the switch. In patients with low PTH (w-PTH less than 90 pg/ml before the switch), continuous increase of w-PTH, BAP, and TRACP-5b was observed. This appeared to be a favorable response because the risk ofadynamic bone disease was high in this group of patients. On the other hand, acute elevation of the 3 parameters was well-controlled in patients with moderate and high PTH (w-PTH from 90 - 180 pg/ml, w-PTH more than 180 pg/ml, respectively) by increased dosage of active VD. CONCLUSION: These results demonstrate that 1.25 mmol/l Ca dialysate improved mineral metabolism by lowering S-Ca and releasing oversuppression of PTH. Our data also suggest that appropriate use of active VD could prevent acute rise of PTH.

Diffusion Tensor Imaging MRI With Spin-Echo Sequence and Long-Duration Measurement for Evaluation of Renal Fibrosis in a Rat Fibrosis Model.

BACKGROUND: Renal fibrosis (RF) is a well-known marker for chronic kidney disease (CKD) progression, including chronic renal injury after renal transplantation. However, invasive biopsy is an available examination for evaluation of RF. Diffusion MRI was once recognized as a promising option for RF. However, it is now controversial for RF evaluation in a unilateral ureteral obstruction (UUO) model. METHODS: To seek an optimal imaging method applicable for RF in UUO model kidneys, we attempted a series of MRI methods, including proton density-weighted imaging, T1-weighted imaging, T2-weighted imaging, T2*-weighted imaging, diffusion-weighted imaging, and diffusion tensor imaging (DTI). RESULTS: We identified DTI MRI by spin-echo sequence plus a special kidney attachment as the best option for evaluation of renal UUO fibrosis, compared with normal kidney on the opposite side. To confirm these results, we applied this technique to a rat UUO therapeutic model with the anti-fibrotic reagent Fasudil. Fractional anisotropy values calculated from DTI MRI showed statistically significant linear correlation with the RF area measured by use of Sirius red or Masson trichrome staining of the positive area [cortex (r = 0.6397, P = .0283) and outer stripe of the outer medulla (r = 0.7810, P = .0039)]. CONCLUSIONS: By use of the DTI MRI with spin-echo sequence, it may be possible to accurately evaluate RF in CKD.

Comparison of topoisomerase I inhibition, DNA damage, and cytotoxicity of camptothecin derivatives presently in clinical trials.

BACKGROUND: Camptothecins belong to a group of anticancer agents with a unique mechanism of action: poisoning of eukaryotic DNA topoisomerase I. Two camptothecin derivatives, topotecan (TPT) and CPT-11, are in clinical trials and their chemotherapeutic efficacy appears promising. PURPOSE: Our aim was to compare simultaneously the molecular and cellular pharmacology of the various camptothecin derivatives that are presently in clinical trials. METHODS: Cytotoxicity of drugs toward human colon carcinoma HT-29 cells was determined by colony-forming assays. DNA single-strand breaks (SSB) were measured by alkaline elution. Drug potency to induce topoisomerase 1-mediated DNA cleavage and the sequence selectivity of the breaks were determined by sequencing gel autoradiography. RESULTS: SN-38 and CPT were more cytotoxic than 9-AC and TPT, and CPT-11 was almost inactive toward HT-29 cells. IC50 values were 8.8 nM for SN-38, 10 nM for CPT, 19 nM for 9-AC, 33 nM for TPT, and greater than 100 nM for CPT-11. In drug-induced DNA damage measured by alkaline elution drug concentrations producing 1000-rad-equivalents (C1000), values were 0.037 microM for SN-38, 0.051 microM for CPT, 0.085 microM for 9-AC, 0.28 microM for TPT, and greater than 1 microM for CPT-11. SN-38 remained the most potent compound in isolated nuclei, and CPT-11 was still inactive. The potency ranking was the same as in whole cells, and the C1000 values were 0.0025 microM for SN-38, 0.012 microM for CPT, 0.021 microM for 9-AC, 0.44 microM for TPT, and greater than 0.1 microM for CPT-11. Potency difference between SN-38 and the other compounds was greater in isolated nuclei than in whole cells. CONCLUSIONS: Kinetics of the reversal of drug-induced SSB in isolated nuclei suggest that dissociation of SN-38 from cleavable complexes is much slower than that of CPT. Cleavage patterns of CPT and 9-AC were similar but differed from those of TPT and SN-38. Although in vitro analyses do not necessarily reflect chemotherapeutic efficacy, this study found that SN-38 is the most potent compound and that 9-AC and TPT are less active than CPT in this system. The effect of CPT-11 is minimal. Therefore, the clinical activity of CPT-11 may strongly depend on its hydrolysis to SN-38. Differences in DNA sequence selectivity and the stability of cleavable complexes induced by the drugs may also contribute to differences among CPT derivatives.