Quasiparticle interference of C2-symmetric surface states in LaOFeAs parent compound

We present scanning tunneling microscopy studies of the LaOFeAs parent compound of iron pnictide superconductors. Topographic imaging reveals two types of atomically flat surfaces, corresponding to the exposed LaO layer and FeAs layer respectively. On one type of surface, we observe strong standing wave patterns induced by quasiparticle interference of two-dimensional surface states. The distribution of scattering wavevectors exhibits pronounced two-fold symmetry, consistent with the nematic electronic structure found in the Ca(Fe1-xCox)2As2 parent state.Comment: 13 pages, 4 figure

Structure and composition of the superconducting phase in alkali iron selenide Ky_yFe1.6+x_{1.6+x}Se2_2

We use neutron diffraction to study the temperature evolution of the average structure and local lattice distortions in insulating and superconducting potassium iron selenide K$_y$Fe$_{1.6+x}$Se$_2$. In the high temperature paramagnetic state, both materials have a single phase with crystal structure similar to that of the BaFe$_2$As$_2$ family of iron pnictides. While the insulating K$_y$Fe$_{1.6+x}$Se$_2$ forms a $\sqrt{5}\times\sqrt{5}$ iron vacancy ordered block antiferromagnetic (AF) structure at low-temperature, the superconducting compounds spontaneously phase separate into an insulating part with $\sqrt{5}\times\sqrt{5}$ iron vacancy order and a superconducting phase with chemical composition of K$_z$Fe$_{2}$Se$_2$ and BaFe$_2$As$_2$ structure. Therefore, superconductivity in alkaline iron selenides arises from alkali deficient K$_z$Fe$_{2}$Se$_2$ in the matrix of the insulating block AF phase.Comment: 10 pages, 5 figure

PREPARATION AND CHARACTERIZATION OF CONDUCTIVE PAPER VIA IN SITU POLYMERIZATION OF 3,4-ETHYLENEDIOXYTHIOPHENE

Conductive paper was prepared via in situ chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in pulp suspension by using iron(III) p-toluenesulfonate (Fe(OTs)3) as both an oxidant and a dopant source. The deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) on the pulp fiber surface was verified and characterized by ATR-FTIR and SEM analyses. The factors affecting the conductivity of the PEDOT-coated paper were investigated, and the preparation conditions of the conductive paper with a low resistivity and excellent environmental stability was obtained. The optimum reaction temperature and time were 60 °C and 4 h, respectively. The molar ratio of EDOT to Fe(OTs)3 of 1:1 was optimal when considering both cost and performance factors. The conductivity of the PEDOT-coated paper could be controlled by adjusting EDOT concentration. The threshold concentration of EDOT was about 3 g•L-1, and a volume resistivity as low as 5.9×103 Ω•cm could be achieved, which reached the conductivity range of an electrical conductor. The environmental stability of the PEDOT-coated conductive paper was very good due to the much higher oxidation potential of PEDOT