We present a consistent overall picture of the electronic structure and ferromagnetic interaction in CaB 6 , based on our joint transport, optical, and tunneling measurements on high-quality defect-controlled single crystals. Pure CaB 6 single crystals, synthesized with 99.9999% pure boron, exhibited fully semiconducting characteristics, such as monotonic resistance for 2-300 K, a tunneling conductance gap, and an optical absorption threshold at 1.0 eV. Boron-related defects formed in CaB 6 single crystals synthesized with 99.9% pure boron induced midgap states 0.18 eV below the conduction band and extra free charge carriers, with the transport, optical, and tunneling properties substantially modified. Remarkably, no ferromagnetic signals were detected from single crystals made with 99.9999% pure boron, regardless of stoichiometry, whereas those made with 99.9% boron exhibited ferromagnetism within a finite range of carrier density. The possible surmise between the electronic state and magnetization will be discussed.

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Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm1.86Ce0.14CuO4 shows a much stronger pseudo-gap or "hot-spot" effect than that observed in other optimally doped n-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that d-wave superconductivity in this compound would be of a novel "nodeless" gap variety. The gross features of the Fermi surface topology and low energy electronic structure are found to be well described by reconstruction of bands by a √ 2× √ 2 order. Comparison of the ARPES and optical data from the same sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap effects. However, the high energy electronic structure is found to be inconsistent with such a scenario. We show that a number of these model inconsistencies can be resolved by considering a short range ordering or inhomogeneous state.PACS numbers: 74.25. Jb, In spite of their many interesting physical properties 1,2,3,4 , electron-doped HTSCs have been much less studied as compared to the hole-doped HTSCs. It was not until a few years ago that high resolution ARPES was applied and there are still only a handful of published papers on the subject. In their high resolution ARPES studies, Armitage et al. found that for the highest T c samples of Nd 1.85 Ce 0.15 CuO 4 (NCCO) the near E F spectral weight was strongly suppressed at the momentum space positions where the underlying Fermi surface (FS) contour crosses the AF Brillouin zone boundary (AFZB) suggesting the existence of a (π,π) scattering channel 5 . It was also found that for (x=0.04) underdoped samples an electron FS pocket exists around (π,0) point and that at higher dopings spectral weight increases near (π/2,π/2) which eventually completes the large hole-like FS pocket around the (π,π) point 6 . A possible way to view the results for the highest-T c samples -at least qualitatively -is as a manifestation of a band reconstruction from a √ 2 × √ 2 static (or slowly fluctuating) spin density wave (SDW) or similar symmetry order 7 . Such a picture explains hot spots on the FS contour as due not to the opening of a 'pseudo-gap' per se but instead due to a band folding and then splitting across the AFZB giving FS pockets around (π/2, π/2) and (π, 0). Such a simple two band interpretation enables one to understand issues such as the sign change in the Hall coefficient 8 and optical conductivity 9 spectra. However, systematic studies to test the model are lacking and there may be doubts that such a simple picture could describe the data at the level of small details.Motivated by these issues, we have performed an extensive high resolution ARPES study on another compound in the small family of electron-doped HTSCs Sm 1.85 Ce 0.15 CuO 4 (SCCO) as well as optical reflection measurements. A quantitative analysis yields a number of important observat...

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