Chalcogen-height dependent magnetic interactions and magnetic order switching in FeSex_xTe1−x_{1-x}

Magnetic properties of iron chalcogenide superconducting materials are investigated using density functional calculations. We find the stability of magnetic phases is very sensitive to the height of chalcogen species from the Fe plane: while FeTe with optimized Te height has the double-stripe-type $(\pi,0)$ magnetic ordering, the single-stripe-type $(\pi,\pi)$ ordering becomes the ground state phase when Te height is lowered below a critical value by, e.g., Se doping. This behavior is understood by opposite Te-height dependences of the superexchange interaction and a longer-range magnetic interaction mediated by itinerant electrons. We also demonstrate a linear temperature dependence of the macroscopic magnetic susceptibility in the single-stripe phase in contrast to a constant behavior in the double-stripe phase. Our findings provide a comprehensive and unified view to understand the magnetism in FeSe$_x$Te$_{1-x}$ and iron pnictide superconductors.Comment: 4 pages, 4 figure

Circulating and persistent currents induced by a current magnification and Aharonov-Casher phase

We considered the circulating current induced by the current magnification and the persistent current induced by Aharonov-Casher flux. The persistent currents have directional dependence on the direct current flow, but the circulating currents have no directional dependence. Hence in the equilibrium, only the persistent current can survives on the ring. For the charge current, the persistent charge current cancelled between spin up and down states, because of the time reversal symmetry of the Hamiltonian on the ring. So there are only circulating charge currents on the ring for electrons with unpolarized spin in the nonequilibrium. However, only the persistent spin currents contributes to the spin currents for electrons with unpolarized spin.Comment: 9 pages and 4 ps figure