Neutron diffraction has been used to study the lattice and magnetic structures of the insulating and superconducting RbyFe1.6+xSe2. For the insulating RbyFe1.6+xSe2, neutron polarization analysis and single crystal neutron diffraction unambiguously confirm the earlier proposed √ 5 × √ 5 block antiferromagnetic structure. For superconducting samples (Tc = 30 K), we find that in addition to the tetragonal √ 5 × √ 5 superlattice structure transition at 513 K, the material develops a separate √ 2 × √ 2 superlattice structure at a lower temperature of 480 K. These results suggest that superconducting RbyFe1.6+xSe2 is phase separated with coexisting √ 2 × √ 2 and √ 5 × √ 5 superlattice structures.

Based on 106×10(6)ψ(3686) events collected with the BESIII detector at the BEPCII facility, a partial wave analysis of ψ(3686)→ppπ0 is performed. The branching fraction of this channel has been determined to be B(ψ(3686)→ppπ0)=(1.65±0.03±0.15)×10(-4). In this decay, 7 N* intermediate resonances are observed. Among these, two new resonances, N(2300) and N(2570) are significant, one 1/2+ resonance with a mass of 2300(-30-0)(+40+109)  MeV/c2 and width of 340(-30-58)(+30+110)  MeV/c2, and one 5/2- resonance with a mass of 2570(-10-10)(+19+34)  MeV/c2 and width of 250(-24-21)(+14+69)  MeV/c2. For the remaining 5 N* intermediate resonances [N(1440), N(1520), N(1535), N(1650) and N(1720)], the analysis yields mass and width values that are consistent with those from established resonances.

The lower critical field H c1 has been carefully measured on a well-shaped cylindrical dense sample of the new superconductor MgB 2 fabricated by high-pressure synthesis. The penetration depth is calculated from the H c1 data. It is found that a linear relation of H c1 (T) appears in the whole temperature region below T c . Furthermore, a finite slope of dH c1 /dT and d(T)/dT remains down to the lowest temperature ͑2 K͒. These are inconsistent with the expectation for an isotropic s-wave superconductivity in MgB 2 .