Bulk quantities of single-crystal Te microtubes have been synthesized by a simple physical evaporation method. Scanning electron microscopy (SEM) revealed the hollow prismatic morphology of the microtubes, which had diameters ranging from about 10 to several hundred micrometers and length up to several centimeters. X-Ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and selected-area electron diffraction (SAED) have been carried out to characterize the tubular structures. It was interesting to find that as-synthesized Te microtubes had an obvious positive magnetoresistance effect at low temperature.

The temperature and frequency dependences of the conductivity derived from optical reflection and transmission measurements of electron-doped ${\text{BaFe}}_2{\text{As}}_2$ crystals and films are analyzed according to gap nodes or possibly a very small gap, or in the crossover region between these two possibilities. This can arise when one of the several pockets known to exist in these systems has extended $s$-wave gap symmetry with an anisotropic piece cancelling or nearly so the isotropic part in some momentum direction. Alternatively, a node can be lifted by impurity scattering which reduces anisotropy. We find that the smaller gap on the hole pocket at the $\Gamma$ point in the Brillouin zone is isotropic $s$ wave while the electron pocket at the $M$ point has a larger gap which is anisotropic and falls in the crossover region. DOI: http://dx.doi.org/10.1103/PhysRevB.82.184527 © 2010 The American Physical Society