XANES study of rare-earth valency in LRu4P12 (L = Ce and Pr)

Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES spectrum suggests that Ce is mainly trivalent, but the 4f state strongly hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does not originate from Pr valence fluctuation.Comment: 4 page

Dysfunction of Protein Quality control in Parkinsonism-Dementia complex of Guam

Guam parkinsonism-dementia complex (G-PDC) is an enigmatic neurodegenerative disease that is endemic to the Pacific island of Guam. G-PDC patients are clinically characterized by progressive cognitive impairment and parkinsonism. Neuropathologically, G-PDC is characterized by abundant neurofibrillary tangles, which are composed of hyperphosphorylated tau, marked deposition of 43-kDa TAR DNA-binding protein, and neuronal loss. Although both genetic and environmental factors have been implicated, the etiology and pathogenesis of G-PDC remain unknown. Recent neuropathological studies have provided new clues about the pathomechanisms involved in G-PDC. For example, deposition of abnormal components of the protein quality control system in brains of G-PDC patients indicates a role for proteostasis imbalance in the disease. This opens up promising avenues for new research on G-PDC and could have important implications for the study of other neurodegenerative disorders.ArticleFRONTIERS IN NEUROLOGY.9:173(2018)journal articl

Infrared study of spin crossover Fe-picolylamine complex

Infrared (IR) absorption spectroscopy has been used to probe the evolution of microscopic vibrational states upon the temperature- and photo-induced spin crossovers in [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic). To overcome the small sizes and the strong IR absorption of the crystal samples used, an IR synchrotron radiation source and an IR microscope have been used. The obtained IR spectra of Fe-pic show large changes between high-spin and low-spin states for both the temperature- and the photo- induced spin crossovers. Although the spectra in the temperature- and photo-induced high-spin states are relatively similar to each other, they show distinct differences below 750 cm-1. This demonstrates that the photo-induced high-spin state involves microscopically different characters from those of the temperature-induced high-spin state. The results are discussed in terms of local pressure and structural deformations within the picolylamine ligands, and in terms of their possible relevance to the development of macroscopic photo-induced phase in Fe-pic.Comment: 6 pages (text) and 6 figures,submitted to J. Phys. Soc. Jp

SET based experiments for HTSC materials: II

The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we further discuss our original suggestion of using Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show if electron is fractionalized in cuprates as indicated by ARPES data. In contrast to flux trapping experiments SET based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P: P10-0

Langevin simulation of the full QCD hadron mass spectrum on a lattice

Langevin simulation of quantum chromodynamics (QCD) on a lattice is carried out fully taking into account the effect of the quark vacuum polarization. It is shown that the Langevin method works well for full QCD and that simulation on a large lattice is practically feasible. A careful study is made of systematic errors arising from a finite Langevin time-step size. The magnitude of the error is found to be significant for light quarks, but the well-controlled extrapolation allows a separation of the values at the vanishing time-step size. As another important ingredient for the feasibility of Langevin simulation the advantage of the matrix inversion algorithm of the preconditioned conjugate residual method is described, as compared with various other algorithms. The results of a hadron-mass-spectrum calculation on a 93×18 lattice at β=5.5 with the Wilson quark action having two flavors are presented. It is shown that the contribution of vacuum quark loops significantly modifies the hadron masses in lattice units, but that the dominant part can be absorbed into a shift of the gauge coupling constant at least for the ground-state hadrons. Some suggestion is also presented for the physical effect of vacuum quark loops for excited hadrons

Charge order, dielectric response and local structure of La5/3Sr1/3NiO4 system

Charge ordering, dielectric permittivity and local structure of La5/3Sr1/3NiO4 system have been explored X-ray charge scattering, complex dielectric impedance spectroscopy, and extended X-ray absorption fine structure (EXAFS) measurements, made on the same single crystal sample. The local structure measured by the temperature dependent polarized Ni K-edge EXAFS shows significant distortions in the NiO2 planes. These local distortions could be reasonable cause of high dielectric permittivity of the title system (e=100 at 5K) with the charge ordering in this system being a ferroelectric-like second order transition.Comment: 12 pages, 5 figure

New superconduting cuprates with no effective doping: T'-(La3+)2-x(RE3+)xCuO4

We report the synthesis of new superconducting cuprates T'-La2-xRExCuO4 (RE = Sm, Eu, Tb, Lu, and Y) using molecular beam epitaxy. The new superconductors have no effective dopant, at least nominally. The substitution of isovalent RE for La was essentially performed to stabilize the T' phase of La2CuO4 instead of the T phase. The maximum Tconset is ~ 25 K and Tczero is ~ 21 K. The keys to our discovery are (1) the preparation of high-crystalline-quality La-based T' films by low-temperature (~ 650C) thin film processes, and (2) more thorough removal of impurity oxygen at the apical site, which is achieved by the larger in-plane lattice constant (a0) of T'-La2-xRExCuO4 than other T'-Ln2CuO4 (Ln = Pr, Nd, Sm, Eu, Gd) with the aid of large surface-to-volume ratio of thin films.Comment: 10 pages, 5 figures (Proceedings of the 16th international symposium on superconductivity (ISS 2003), to be published in Physica C