Gapped Collective Charge Excitations and Interlayer Hopping in Cuprate Superconductors.

We use resonant inelastic x-ray scattering to probe the propagation of plasmons in the electron-doped cuprate superconductor Sr_{0.9}La_{0.1}CuO_{2}. We detect a plasmon gap of ∼120 meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in Sr_{0.9}La_{0.1}CuO_{2} are not strictly acoustic. The plasmon dispersion, including the gap, is accurately captured by layered t-J-V model calculations. A similar analysis performed on recent resonant inelastic x-ray scattering data from other cuprates suggests that the plasmon gap is generic and its size is related to the magnitude of the interlayer hopping t_{z}. Our work signifies the three dimensionality of the charge dynamics in layered cuprates and provides a new method to determine t_{z}.

Testosterone: activation or organization of spatial cognition?

Previous studies in animals have revealed effects of both prenatal and current testosterone on brain organization and behavior. However, it is unclear how these effects translate to the human brain. Here, we refine previous procedures to clarify the relative contribution of prenatal versus current testosterone indices to cognitive function. Sixty-nine subjects performed four computerized tasks measuring mental rotation, targeting, figure-disembedding and perceptual discrimination. Using stepwise regression analyses, performance was related to free testosterone assayed in saliva samples and to second-to-fourth finger length ratios (2D:4D), a putative index of prenatal testosterone exposure. The exclusive predictor for mental rotation was found to be sex, while 2D:4D was found to be the sole predictor of targeting, exhibiting a curvilinear relation, and figure-disembedding performance, showing a linear relation. These findings suggest a substantial role for prenatal testosterone but not current testosterone in determining cognitive performance.