24 research outputs found

    Cooperative dynamics in doped manganite films: phonon anomalies in the ferromagnetic state

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    We present optical measurements of phononic excitations in La2/3_{2/3}Ca1/3_{1/3}MnO3_{3} (LCMO) and La2/3_{2/3}Sr1/3_{1/3}MnO3_{3} (LSMO) thin films covering the full temperature range from the metallic ferromagnetic to the insulating paramagnetic phase. All eight phonons expected for the R3ˉ\bar{3}c symmetry in LSMO and 17 out of the expected 25 phonons for the Pnma symmetry in LCMO have been determined. Close to the ferromagnetic-to-paramagnetic transition both compounds reveal an anomalous behavior but with different characteristics. Anomalies in the phononic spectra are a manifestation of the coupling of lattice degrees of freedom (DOF) to electronic DOF. Specifically, the low-frequency external group proves to be an indicator for lattice modifications induced by electronic correlations. The enhanced electron-phonon coupling in LCMO is responsible for Fano-like interference effects of distinct phonon modes with electronic continuum excitations: we observe asymmetric phonon line shapes, mode splitting and spectral weight transfer between modes.Comment: 10 pages, 10 figure

    Large and Small Polaron Excitations in La2/3(Sr/Ca)1/3MnO3 Films

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    We present detailed optical measurements of the mid-infrared (MIR) excitations in thin films of La2/3Sr1/3MnO3 (LSMO) and La2/3Ca1/3MnO3 (LCMO) across the magnetic transition. The shape of the excitation at about 0.2 eV in both samples is analyzed in terms of polaron models. We propose to identify the MIR resonance in LSMO as the excitation of large polarons and that in LCMO as a small polaron excitation. A scaling behavior for the low-energy side of the polaronic MIR resonance in LSMO is established

    Phonon-Metamorphosis in Ferromagnetic Manganite Films: Probing the Evolution of an Inhomogeneous State

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    The analysis of phonon anomalies provides valuable information about the cooperative dynamics of lattice, spin and charge degrees of freedom. Significant is the anomalous temperature dependence of the external modes observed in La2/3_{2/3}Sr1/3_{1/3}MnO3_{3} (LSMO) films. The two external modes merge close to the ferromagnetic to paramagnetic transition at TCT_C and, moreover, two new modes evolve in this temperature range with strong resonances at slightly higher frequencies. We propose that this observed phonon metamorphosis probes the inhomogeneous Jahn-Teller distortion, manifest on the temperature scale TCT_C. The analysis is based on the first observation of all eight phonon modes in the metallic phase of LSMO and on susceptibility measurements which identify a Griffiths-like phase.Comment: 4 pages, 4 figure

    Polaronic excitations in CMR manganite films

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    In the colossal magnetoresistance manganites polarons have been proposed as the charge carrier state which localizes across the metal-insulator transition. The character of the polarons is still under debate. We present an assessment of measurements which identify polarons in the metallic state of La{2/3}Sr{1/3}MnO{3} (LSMO) and La{2/3}Ca{1/3}MnO{3} (LCMO) thin films. We focus on optical spectroscopy in these films which displays a pronounced resonance in the mid-infrared. The temperature dependent resonance has been previously assigned to polaron excitations. These polaronic resonances are qualitatively distinct in LSMO and LCMO and we discuss large and small polaron scenarios which have been proposed so far. There is evidence for a large polaron excitation in LSMO and small polarons in LCMO. These scenarios are examined with respect to further experimental probes, specifically charge carrier mobility (Hall-effect measurements) and high-temperature dc-resistivity.Comment: 16 pages, 10 figure

    Elemental and chemically specific x-ray fluorescence imaging of biological systems

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    Raman study of ordering phenomena in copper–oxygen systems

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    We summarize results of light-scattering experiments in underdoped La2−xSrxCuO4 (LSCO) and YBa2Cu3O6+x (Y-123) single crystals. Below a doping-dependent temperature close to the pseudogap cross-over line T*(p) new peaks appear in the low-energy part of the spectra. For low doping, p0.02 holes per CuO2, the features are observed in B2g symmetry in both LSCO and Y-123. At p=0.10 the additional contribution exists only in LSCO and is found at B1g symmetry. We interpret the low-energy peaks in terms of a charge ordering instability. The ‘stripes’ are fluctuating with preferential orientation along the diagonals and the principle axes at p0.02 and p=0.10, respectively

    Artesunate und seine Derivate in der Anwendung gegen die HNSCC Zelllinie (UMSCC1)

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    Einleitung: Die Traditionelle Chinesische Medizin fundiert auf einer ca. 5000 Jahre alten Erfahrung mit medizinischen Heilpflanzen. Unter diesen findet Artemisinin, die Grundsubstanz aus der Artemisia annua L., nicht nur Anwendung in der Malaria Behandlung, sondern auch in der Krebsbehandlung. Aus diesem Grund haben wir eine Reihe von Artemisinin-Derivaten (Artesunate) auf ihre anti-tumoröse Wirkung geprüft und deren Aktivität mit denen von etablierten Zytostatika als Kontrollen verglichen. Material und Methoden: Artesunate (ART) wurde von Saokim Ltd (Hanoi, Vietnam) und 24 Artesunate-Derivate von ElSohly (NCI, USA) zur Verfügung gestellt. Cisplatin, 5-fluorouracil (5-FU), Carboplatin und Docetaxel wurden von der Klinikapotheke der Universitätsklinik Heidelberg ausgehändigt. Als Test-Modell benutzten wir die etablierte Plattenepithel-Carcinom-Zelllinie eines Kopf-Hals-Tumors (Mundboden-Ca, T2N0M0), UMSCC1. Die Aktivität der Zytotoxizität dieser Verbindungen wurde mit dem XTT-Test (Roche) getestet.Ergebnisse: Artesunate zeigte eine IC50 von 25 µM, exemplarisch zeigten ART-Derivat 72-4 IC50=19,8 µM und ART-Derivat 9-1 IC50=17,9 µM. Docetaxel IC50=0.015 M. Hingegen, wurden keine zytotoxischen Effekte mit den Chemotherapeutika 5-FU, Carboplatin und Cisplatin in den Konzentrationen 10-5-10-9,5 M beobachtet. Schlussfolgerung: Die Toxizität nimmt mit den Artesunate-Derivaten im Vergleich zu den klinisch angewendeten Chemotherapeutika gegenüber der UMSCC1 Tumorzellen zu. Artesunate und seine Derivate haben somit ein höheres zyotoxisches Potential als 5-Fu, Carboplatin und Cisplatin. Weiterführende Analysen sind derzeit in Arbeit, um die verantwortlichen Molekularbiologischen Mechanismen für die zytotoxische Wirkung der Verbindungen aufzuklären
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