Magnetic and transport properties of the spin-state disordered oxide La0.8Sr0.2Co_{1-x}Rh_xO_{3-\delta}

We report measurements and analysis of magnetization, resistivity and thermopower of polycrystalline samples of the perovskite-type Co/Rh oxide La$_{0.8}$Sr$_{0.2}$Co$_{1-x}$Rh$_x$O$_{3-\delta}$. This system constitutes a solid solution for a full range of $x$,in which the crystal structure changes from rhombohedral to orthorhombic symmetry with increasing Rh content $x$. The magnetization data reveal that the magnetic ground state immediately changes upon Rh substitution from ferromagnetic to paramagnetic with increasing $x$ near 0.25, which is close to the structural phase boundary. We find that one substituted Rh ion diminishes the saturation moment by 9 $\mu_B$, which implies that one Rh$^{3+}$ ion makes a few magnetic Co$^{3+}$ ions nonmagnetic (the low spin state), and causes disorder in the spin state and the highest occupied orbital. In this disordered composition ($0.05\le x \le 0.75$), we find that the thermopower is anomalously enhanced below 50 K. In particular, the thermopower of $x$=0.5 is larger by a factor of 10 than those of $x$=0 and 1, and the temperature coefficient reaches 4 $\mu$V/K$^2$ which is as large as that of heavy-fermion materials such as CeRu$_2$Si$_2$.Comment: 8 pages, 6 figures, accepted to Phys. Rev.

Multivalued memory effects in electronic phase-change manganites controlled by Joule heating

Non-volatile multivalued memory effects caused by magnetic fields, currents, and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and (Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic region between ferromagnetic metallic and charge-ordered insulating states. The current/voltage effects observed in this study are explained by the self-heating effect, which enable us to control the colossal electroresistance effects. This thermal-cycle induced switching between electronic solid and liquid states can be regarded as electronic version of atomic crystal/amorphous transitions in phase-change chalcogenides.Comment: 5 pages, 4 figures. to appear in Phys. Rev.

Crystallographic and superconducting properties of the fully-gapped noncentrosymmetric 5d-electron superconductors CaMSi3 (M=Ir, Pt)

We report crystallographic, specific heat, transport, and magnetic properties of the recently discovered noncentrosymmetric 5d-electron superconductors CaIrSi3 (Tc = 3.6 K) and CaPtSi3 (Tc = 2.3 K). The specific heat suggests that these superconductors are fully gapped. The upper critical fields are less than 1 T, consistent with limitation by conventional orbital depairing. High, non-Pauli-limited {\mu}0 Hc2 values, often taken as a key signature of novel noncentrosymmetric physics, are not observed in these materials because the high carrier masses required to suppress orbital depairing and reveal the violated Pauli limit are not present.Comment: 8 pages, 8 figure

Die diabetische Retinopathie und ihre Behandlung mit Lichtkoagulation

Jedes 8.rztliche Handeln sttitzt sich auf folgende Voraussetzungen: Das Krankheitsbild unseres Patienten ist bekannt, und wir sind sicher, dass sein natilrlicher Verlauf ungtinstige Folgen haben wird. Die Mittel bestehen, dieses Krankheitsbild giinstig zu beeinflussen, und wir sind in der Lage, sie ohne Schaden anzuwenden. Die Frage, ob diese Voraussetzungen fiir die Behandlung der diabetischen Retinopathie heute gegeben sind, kann leider immer noch nicht mit einem eindeutigen Ja beantwortet werden; und doch wird an vielen Stellen der Welt die diabetische Retinopathie behandelt uberall, wo man glaubt, Mittel zu besitzen, die belfen kOnnen, und wo man nicht passiv zuschauen mochte, wie Menschen blind werden. Die vorliegende Arbeit soil versuchen, anhand der bisherigen Publikationen in Ki.irze das vorhandene Wissen tiber Pathogenese, Klinik und Verlauf der diabetischen Retinopathie zusammenzufassen. Weiter will sie versuchen darzustellen, was tiber die Wirksamkeit der bisherigen Behandlungsmethoden bekannt ist und in wieweit wir heute diese Erfahrungen als Basis fiir unsere therapeutischen Indikationen gebrauchen di.irfen. Ihr Hauptteil ist der Behandlung der diabetischen Retinopathie mit Lichtkoagulation gewidmet. Er enthaJt die Erfahrungen, die bei der Behandlung und Kontrolle von 177 Patienten im Augenkrankenhaus in Rotterdam im Verlauf van 4 Jahren gesammelt wurden

Imaging Oxygen Defects and their Motion at a Manganite Surface

Manganites are technologically important materials, used widely as solid oxide fuel cell cathodes: they have also been shown to exhibit electroresistance. Oxygen bulk diffusion and surface exchange processes are critical for catalytic action, and numerous studies of manganites have linked electroresistance to electrochemical oxygen migration. Direct imaging of individual oxygen defects is needed to underpin understanding of these important processes. It is not currently possible to collect the required images in the bulk, but scanning tunnelling microscopy could provide such data for surfaces. Here we show the first atomic resolution images of oxygen defects at a manganite surface. Our experiments also reveal defect dynamics, including oxygen adatom migration, vacancy-adatom recombination and adatom bistability. Beyond providing an experimental basis for testing models describing the microscopics of oxygen migration at transition metal oxide interfaces, our work resolves the long-standing puzzle of why scanning tunnelling microscopy is more challenging for layered manganites than for cuprates.Comment: 7 figure

Odd-frequency Pairs and Josephson Current through a Strong Ferromagnet

We study Josephson current in superconductor / diffusive ferromagnet /superconductor junctions by using the recursive Green function method. When the exchange potential in a ferromagnet is sufficiently large as compared to the pair potential in a superconductor, an ensemble average of Josephson current is much smaller than its mesoscopic fluctuations. The Josephson current vanishes when the exchange potential is extremely large so that a ferromagnet is half-metallic. Spin-flip scattering at junction interfaces drastically changes the characteristic behavior of Josephson current. In addition to spin-singlet Cooper pairs, equal-spin triplet pairs penetrate into a half metal. Such equal-spin pairs have an unusual symmetry property called odd-frequency symmetry and carry the Josephson current through a half metal. The penetration of odd-frequency pairs into a half metal enhances the low energy quasiparticle density of states, which could be detected experimentally by scanning tunneling spectroscopy. We will also show that odd-frequency pairs in a half metal cause a nonmonotonic temperature dependence of the critical Josephson current.Comment: 12 pages 14 figures embedde

Magnetic Ground State of Pr0.89_{0.89}LaCe0.11_{0.11}CuO4+α−δ_{4+\alpha-\delta} with Varied Oxygen Depletion Probed by Muon Spin Relaxation

The magnetic ground state of an electron-doped cuprate superconductor Pr$_{1-x}$LaCe$_x$CuO$_{4+\alpha-\delta}$ ($x=0.11, \alpha\simeq0.04$) has been studied by means of muon spin rotation/relaxation (\msr) over a wide variety of oxygen depletion, $0.03\le\delta\le0.12$. Appearance of weak random magnetism over entire crystal volume has been revealed by a slow exponential relaxation. The absence of $\delta$-dependence for the random magnetism and the multiplet pattern of muon Knight shift at higher fields strongly suggest that the random moments are associated with excited Pr$^{3+}$ ions under crystal electric field.Comment: 6 pages, 4 figures, submitted to J. Phys. Soc. Jp