10,077 research outputs found

    Anisotropic superconducting properties of aligned Sm0.95_{0.95}La0.05_{0.05}FeAsO0.85_{0.85}F0.15_{0.15} microcrystalline powder

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    The Sm0.95_{0.95}La0.05_{0.05}FeAsO0.85_{0.85}F0.15_{0.15} compound is a quasi-2D layered superconductor with a superconducting transition temperature Tc_c = 52 K. Due to the Fe spin-orbital related anisotropic exchange coupling (antiferromagnetic or ferromagnetic fluctuation), the tetragonal microcrystalline powder can be aligned at room temperature using the field-rotation method where the tetragonal ab\it{ab}-plane is parallel to the aligned magnetic field Ba_{a} and c\it{c}-axis along the rotation axis. Anisotropic superconducting properties with anisotropic diamagnetic ratio χc/χab∼\chi_{c}/\chi_{ab}\sim 2.4 + 0.6 was observed from low field susceptibility χ\chi(T) and magnetization M(Ba_{a}). The anisotropic low-field phase diagram with the variation of lower critical field gives a zero-temperature penetration depth λc\lambda_{c}(0) = 280 nm and λab\lambda_{ab}(0) = 120 nm. The magnetic fluctuation used for powder alignment at 300 K may be related with the pairing mechanism of superconductivity at lower temperature.Comment: 4 pages, 6 figure

    Symmetry Constraints and the Electronic Structures of a Quantum Dot with Thirteen Electrons

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    The symmetry constraints imposing on the quantum states of a dot with 13 electrons has been investigated. Based on this study, the favorable structures (FSs) of each state has been identified. Numerical calculations have been performed to inspect the role played by the FSs. It was found that, if a first-state has a remarkably competitive FS, this FS would be pursued and the state would be crystal-like and have a specific core-ring structure associated with the FS. The magic numbers are found to be closely related to the FSs.Comment: 13 pages, 5 figure
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