Observations of solar energetic particles at a synchronous orbit

The Space Environment Monitors (SEM) on board the Japanese geostationary meteorological satellites (GMS-1 and GMS-2) observed energetic protons, alpha particles and electrons continuously for February 1978 to September 1984. The satellites were at 6.6 Earth radii above 140 deg E equator

Post density functional theoretical studies of highly polar semiconductive Pb(Ti1−x_{1-x}Nix_{x})O3−x_{3-x} solid solutions: The effects of cation arrangement on band gap

We use a combination of conventional density functional theory (DFT) and post-DFT methods, including the local density approximation plus Hubbard $U$ (LDA+$U$), PBE0, and self-consistent $GW$ to study the electronic properties of Ni-substituted PbTiO$_{3}$ (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO$_{2}$ layer. Accurate treatment of localized states in transition-metal oxides like Ni-PTO requires post-DFT methods. $B$-site Ni/Ti cation ordering is also investigated. The $B$-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap ($E_{\rm g}$) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO$_{3}$. This combination of properties make Ni-PTO solid solutions promising candidate materials for solar energy conversion devices.Comment: 19 pages, 6 figure

Full-gap superconductivity robust against disorder in heavy-fermion CeCu2Si2

A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor CeCu$_2$Si$_2$ were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth $\lambda(T)$ in CeCu$_2$Si$_2$. We find that the fully-gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for $s_{++}$-wave superconductivity without sign reversal.Comment: 5 pages, 4 figures + Supplemental Material (1 page, 1 figure). Will appear in Phys. Rev. Let

In-situ growth of superconducting NdFeAs(O,F) thin films by Molecular Beam Epitaxy

The recently discovered high temperature superconductor F-doped LaFeAsO and related compounds represent a new class of superconductors with the highest transition temperature (Tc) apart from the cuprates. The studies ongoing worldwide are revealing that these Fe-based superconductors are forming a unique class of materials that are interesting from the viewpoint of applications. To exploit the high potential of the Fe-based superconductors for device applications, it is indispensable to establish a process that enables the growth of high quality thin films. Efforts of thin film preparation started soon after the discovery of Fe-based superconductors, but none of the earlier attempts had succeeded in an in-situ growth of a superconducting film of LnFeAs(O,F) (Ln=lanthanide), which exhibits the highest Tc to date among the Fe-based superconductors. Here, we report on the successful growth of NdFeAs(O,F) thin films on GaAs substrates, which showed well-defined superconducting transitions up to 48 K without the need of an ex-situ heat treatment