Spectral broadening due to long-range Coulomb interactions in the molecular metal TTF-TCNQ

We employ density-functional theory to calculate realistic parameters for an extended Hubbard model of the molecular metal TTF-TCNQ. Considering both intra- and intermolecular screening in the crystal, we confirm the importance of the suspected longer-range Coulomb interactions along the molecular stacks, as well as inter-stack coupling. Contrary to past belief, these terms do not lead to the formation of a Wigner lattice, but simply broaden the spectral function.     

Magnetic barrier in a two-dimensional hole gas

Transport properties of a magnetic barrier in a Ga_xAl_1−xAs based two-dimensional hole gas are reported. A ferromagnetic cobalt film, separated by an AlO_x layer from the semiconductor in order to prevent leakage currents, is magnetized in-plane, such that the fringe field generates a localized perpendicular magnetic field acting as a magnetic barrier. The resistance as a function of the in-plane magnetic field shows a characteristic minimum at the coercive field of the ferromagnetic film. Semiclassical simulations based on the Landauer–Büttiker formalism show good agreement with the experiment.