Search

Reports on the synthesis of stable fullerides A3C70 (A = Sm,Ba) using solid-state reaction. Monoclinic structure of Sm3C70; Synchrotron powder diffractometry; Derivation of the structure of Ba3C70 from the A15 structure adopted by Ba3C60; Low symmetry relative to C60 fullerides; Absence of superconductivity in C70 fullerides.

Abstract: The ac susceptibility of single crystalline tetragonal EuFe2As2, EuFe2As1.4P0.6, and EuFe1.715Co0.285As2 has been measured over the temperature and hydrostatic (He-gas) pressure ranges 10–60K and 0–0.8GPa, respectively. For all three samples the magnetic ordering temperature (17–19K) from the Eu sublattice increases linearly with pressure, presumably due to the enhanced exchange coupling between Eu-layers. No evidence for a superconducting transition was observed in the susceptibility for any sample over the measured temperature/pressure range. [Copyright &y& Elsevier]

Abstract: 75As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P=4.7 and 10.8kbar, the temperature dependence of nuclear-spin-lattice relaxation rate (1/T 1) measured at tetragonal phase show no coherence peak just below T c and decrease with decreasing temperature. The superconductivity is of gapless at P=4.7kbar but evolves to multiple gaps at P=10.8kbar. We find that the superconductivity appears near a quantum critical point. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound. [Copyright &y& Elsevier]

Abstract: The superconducting gap in FeAs-based superconductor SmFeAs(O1− x F x ) (x =0.15 and 0.30) and the temperature dependence of the sample with x =0.15 have been measured by Andreev reflection spectroscopy. The intrinsic superconducting gap is independent of contacts while many other “gap-like” features vary appreciably for different contacts. The determined gap value of 2Δ =13.34±0.47meV for SmFeAs(O0.85F0.15) gives 2Δ/kBTC =3.68, close to the BCS prediction of 3.53. The superconducting gap decreases with temperature and vanishes at TC , in a manner similar to the BCS behavior but dramatically different from that of the nodal pseudogap behavior in cuprate superconductors. [Copyright &y& Elsevier]

Abstract: To clarify the gap structure of the iron–pnictide superconductors, we synthesized optimally doped single crystals of BaFe1.8Co0.2As2, which had a critical temperature, Tc , of 23.6K. The initial M–H curve was used to find the lower critical field, Hc 1. The full range of the temperature dependence of Hc 1 was explained by using a two S-wave gap symmetry. We estimate the two gap as Δ 1(0)=1.64±0.2meV for the small gap and Δ 2(0)=6.20±0.2meV for the large gap. [ABSTRACT FROM AUTHOR]