Scientists have observed for the first-time changes in magnetic order that point to an important interplay between rare-earth and iron magnetism in rare-earth iron arsenide superconductors. Magnetism is believed to play a key role in causing superconductivity in this class of high-temperature superconductors. Large single crystals and x-ray and neutron techniques in combination with magnetization and electric transport measurements enabled this discovery.
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Researchers have shown that the same atom can have different roles in magnetism, depending on its location in the crystal structure. The complex metallic compound Gd5Ge4 has a crystal structure with three distinct sites for its gadolinium atoms.
Magnetic field is expelled from the bulk of a superconductor and only remains present in a surface layer called London penetration depth, λ. Precision measurements of this quantity provide insight into the structure of the superconducting gap and, ultimately, into the mechanism of superconductivity.
For the first time, conduction electrons in iron arsenide superconductors were determined to reveal unusual anisotropy in the crystallographically-isotropic state—nematic liquid crystalline phase— similar to crystallographic organization of materials used in liquid-crystalline displays. A close relationship between the occurrence of the high-temperature superconductivity and the existence of this unusual nematic electronic phase has been discovered.
Directional heat flow has been used as a probe of the symmetry of a carefully modified barium iron arsenide, superconductor, revealing features that have eluded other experimental methods. Superconductivity occurs because electrons form pairs that are trapped by an energy gap (or gaps) that the electrons cannot occupy. Depending on the direction in which an electron pair is moving, these gaps can be large, small, or even not exist at all.
We report a femtosecond midinfrared study of the broadband low-energy response of individually separated (6,5) and (7,5) single-walled carbon nanotubes. Strong photoinduced absorption is observed around 200 meV, whose transition energy, oscillator strength, resonant chirality enhancement, and dynamics manifest the observation of quasi-one-dimensional intraexcitonic transitions. A model of the nanotube 1s-2p cross section agrees well with the signal amplitudes.
Fig. 1. Inelastic neutron scattering study of superconducting Ba(Fe0.926Co0.074)2As2 reveals anisotropic and quasi-two-dimensional magnetic fluctuations as well as novel quasi-propagating excitations at higher energies.
Fig. 1. Interface energy between a normal and superconducting region at the coexistence magnetic field as function of the ratio of the penetration and coherence length. Positive (negative) values imply Type I (II) superconductivity.
Scientists have discovered a way to make strong materials that are also ductile.