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Rare-Earth and Iron Magnetism Duke It Out in a High-Temperature Superconductor

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.

Discovery of Intrinsic Electronic Anisotropy of Iron Pnictides and Nematic Electronic Order in BaFe2As2

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.

Using Heat to Probe Cool Materials

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.

Ultrafast Spectroscopy of Midinfrared Internal Exciton Transitions in Separated Single-Walled Carbon Nanotubes

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.


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