We report on the electronic, transport, and magnetic properties of the Ce-doped manganite, La1−xCexMnO3. This material is remarkably similar to the heavily investigated hole doped manganite La1−xCaxMnO3; e.g., both materials show Curie temperatures of TC∼250 K for x=0.3. The main difference which makes the Ce-doped material highly interesting for basic research as well as for possible applications (e.g., in spintronics) is the fact that Ce doping drives the manganese in a mixture of Mn2+ and Mn3+ induced by electron doping. We present conclusive evidence for electron doping by x-ray absorption spectroscopy and Hall measurements on single phase epitaxial thin films. From transport measurements on a series of La1−xCexMnO3, the magnetic phase diagram of La1−xCexMnO3 is established.

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We present first measurements of quantum oscillations in the layered oxide superconductor Ag5Pb2O6. From a detailed angular and temperature dependent study of the de Haas-van Alphen effect we determine the electronic structure and demonstrate that the electron masses are very light, m* approximately 1.2me. The Fermi surface we observe is essentially that expected of nearly free electrons--establishing Ag5Pb2O6 as the first known example of a monovalent, nearly free electron superconductor at ambient pressure.

We measured the Fermi surface of the recently discovered superconductor Ag5Pb2O6 via a de Haas-van Alphen rotation study. Two frequency branches were observed and identified with the neck and belly orbits of a very simple, nearly free electron Fermi surface. We use the observed Fermi surface geometry to quantitatively deduce superconducting properties such as the in-plane and out-of-plane penetration depths, the coherence length in the clean limit, and the critical field; as well as normal state properties such as the specific heat and the resistivity anisotropy.

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