Microwave penetration depth and quasiparticle conductivity of PrFeAsO1-y single crystals: evidence for a full-gap superconductor

In-plane microwave penetration depth lambda_{ab} and quasiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO_{1-y} (T_{c} approximately 35 K) by using a sensitive superconducting cavity resonator. lambda_{ab}(T) shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap Delta(k). The temperature dependence of the superfluid density demonstrates that the gap is nonzero (Delta/k_{B}T_{c} greater, similar1.6) all over the Fermi surface. The microwave conductivity below T_{c} exhibits an enhancement larger than the coherence peak, reminiscent of high-T_{c} cuprate superconductors.

The synthesis and structure of suspended ultra-thin Si(3)N(4) nanosheets

Suspended Si(3)N(4) nanosheets at least 4 µm in width and ranging from 1.5 to 4 nm in thickness were successfully synthesized for the first time. Several of those nanosheets had scrolled edges due to being ultra-thin. According to transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations, the Si(3)N(4) nanosheets exhibit microscopic corrugations in the range of several tens of nanometres. In addition, the directions of the microscopic corrugations were not random, but instead parallel to specific crystal orientations.

Local lattice distortion in the giant negative thermal expansion material Mn3Cu1-xGexN

Giant negative thermal expansion is achieved in antiperovskite manganese nitrides when the sharp volume change associated with magnetic ordering is broadened by substitution. In this Letter, we address the unique role of the ''magic" element, Ge, for such broadening in Mn3Cu1-xGexN. We present evidence for a local lattice distortion well described by the low-temperature tetragonal (T4) structure of Mn3GeN for a range of x, where the overall structure remains cubic. This structural instability shows a strong correlation with the broadness of the growth of the ordered magnetic moment and, hence, is considered to trigger the broadening of the volume change.

Origin of the Monoclinic-to-Monoclinic Phase Transition and Evidence for the Centrosymmetric Crystal Structure of BiMnO3

Structural properties of polycrystalline single-phased BiMnO3 samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO3 crystallizes in the centrosymmetric space group C2/c at 300 K. The crystallographic data are a = 9.5415(2) A, b = 5.61263(8) A, c = 9.8632(2) A, beta = 110.6584(12) degrees at 300 K and a = 9.5866(3) A, b = 5.59903(15) A, c = 9.7427(3) A, beta = 108.601(2) degrees at 550 K, Z = 8, space group C2/c. The analysis of Mn-O bond lengths suggested that the orbital order present in BiMnO3 at 300 K melts above TOO = 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature, mueff = 4.69 microB and theta = 138.0 K at 300-450 K and mueff = 4.79 microB and theta = 132.6 K at 480-600 K.