Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our...

We report a significant enhancement of the upper critical field Hc2 of different MgB2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities ρ, we show a clear trend of an increase in Hc2 as ρ increases. One particular high resistivity film had a zero-temperature Hc2(0) well above the Hc2 values of competing non-cuprate superconductors ...

The microwave surface impedance = + 0 of MgB2 thin films was measured via advanced dielectric resonator (DR) techniques. First, the temperature dependence of the penetration depth measured with a sapphire puck at 17.9 GHz can be well fitted from 5 K close to by the standard BCS integral expression assuming the reduced energy gap (0) to be as low as 1.0–1.1 assuming (0) = 100–110 nm. These resul...

Temperature dependent Raman scattering studies in polycrystalline MgB2 (10 < T < 300 K) reveal that the E2g phonon does not experience any self energy renormalization effect across the superconducting critical temperature TC ≈ 40 K, in contrast with most of the current theoretical models. In the presence of our results, those models must be reviewed. The analysis of the temperature dependence o...

The terahertz (THz) range is very attractive for astronomical observations. Spectroscopy and photometry of remote space objects in the THz range allows for a study of their chemical composition, because this range covers rotational lines from simple molecules and electron transition lines from atoms and ions. Heterodyne receivers, due to their high spectral resolution, in the THz range allows f...

0921-4534/$ see front matter 2009 Elsevier B.V. A doi:10.1016/j.physc.2009.10.051 * Corresponding author. E-mail address: [email protected] (M. Eisterer). The influence of two important features of magnesium diboride on the macroscopic transport properties of polycrystalline MgB2 is discussed in the framework of a percolation model. While two band superconductivity does not have significant co...

By synthesizing MgB2 using boron of different nominal purity we found values of the residual resistivity ratio (RRR = R(300K)/R(42K)) from 4 to 20, which covers almost all values found in literature. To obtain high values of RRR, high purity reagents are necessary. With the isotopically pure boron we obtained the highest RRR ∼ 20 for the stoichiometric compound. We also investigated Mgx 11B2 sa...

In this study, we focused on the estimation of the global critical current density, super-current path, grain connectivity and their relationships with the faults volume fraction in the MgB2 bulks prepared by a modified PIT (powder in tube) method. Campbell’s method was applied for the purpose of acquiring the penetrating AC magnetic flux profile and the characteristic of AC magnetic field vs. ...

The powder-in-tube MgB2 wires were prepared by high energy milling of Mg and B powder. The powder was not mechanically alloyed for 2h short milling time. However, the MgB2 grains in wires are very small (20 100nm) and resembled to the dimple after post-heat treatment. The clear evidence for transcrystlline fracture is observed. It indicated that the grain connection was greatly improved and the...