The new alpha-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe(2)As(2) families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (pi, 0), a completely different magnetic order with a composition tunable propagation vector (deltapi, deltapi) was determined for the parent compound Fe_{1+y}Te in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest T_{C} sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

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We show that the quasi-skutterudite superconductor Sr(3)Ir(4)Sn(13) undergoes a structural transition from a simple cubic parent structure, the I phase, to a superlattice variant, the I' phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T(*) can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.

We have determined the resistive upper critical field H c2 for single crystals of the superconductor Fe 1.11 Te 0.6 Se 0.4 using pulsed magnetic fields of up to 60 T. A rather high zero-temperature upper critical field of 0 H c2 ͑0͒Ϸ47 T is obtained in spite of the relatively low superconducting transition temperature ͑T c Ϸ 14 K͒. Moreover, H c2 follows an unusual temperature dependence, becoming almost independent of the magnetic field orientation as the temperature T → 0. We suggest that the isotropic superconductivity in Fe 1.11 Te 0.6 Se 0.4 is a consequence of its three-dimensional Fermi-surface topology. An analogous result was obtained for ͑Ba, K͒Fe 2 As 2 , indicating that all layered iron-based superconductors exhibit generic behavior that is significantly different from that of the "high-T c " cuprates.