We report a systematic increase of the superconducting transition temperature T(c) with a biaxial tensile strain in MgB2 films to well beyond the bulk value. The tensile strain increases with the MgB2 film thickness, caused primarily by the coalescence of initially nucleated discrete islands (the Volmer-Weber growth mode.) The T(c) increase was observed in epitaxial films on SiC and sapphire su...

Measurements of 10 GHz microwave surface resistance, Rs , of dense MgB2 wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure Bardeen–Cooper–Schrieffer s-wave superconductor. However, the Rs ~20 K! of the wire is an order of magnitude lower than that of polycrystal YBa2Cu3...

The dependence of Tc on pure hydrostatic pressure has been determined for the first time on the recently discovered superconductor MgB2 . Using a He-gas apparatus, we find that Tc decreases under pressure to 0.5 GPa at a significantly smaller rate, dTc/dP ≃ −1.11± 0.02 K/GPa, than found in other studies under less hydrostatic pressure conditions. The value of the logarithmic volume derivative, ...

We present results of experimental study of the gain bandwidth (GBW) of MgB2 hot electron-bolometer (HEB) mixers at 0.1THz and 0.4THz. Antenna integrated 0.25-1.5um2 area devices were made from thin MgB2 films deposited with a custom made HPCVD system. Film as thin as 15-45nm had a Tc from 35K to 40K. The GBW was found to be independent on the bias conditions, the bath temperature, and the LO f...

The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy dif...

The dependence of Tc on hydrostatic (He-gas) pressure for superconducting MgB2 has been determined to 0.7 GPa. We find that Tc decreases linearly and reversibly under pressure at the rate dTc/dP ≃ −1.11 ± 0.02 K/GPa. These studies were carried out on the same sample used in earlier structural studies under He-gas pressure which yielded the bulk modulus B = 147.2± 0.7 GPa. The value of the logar...

The recent discovery of superconductivity at ~39 K in MgB2, by Nagamatsu et al.1 establishes this simple binary compound as having the highest bulk superconducting transition temperature, Tc, of any non-copper-oxide material. Much of the initial research has focused on whether MgB2 is a conventional BCS, electron-phonon mediated superconductor, and, if it is, why Tc is so high. Isotope effect m...