Superconductivity in dense MgB2 wires

MgB2 becomes superconducting just below 40 K. Whereas porous polycrystalline samples of MgB2 can be synthesized from boron powders, in this Letter we demonstrate that dense wires of MgB2 can be prepared by exposing boron filaments to Mg vapor. The resulting wires have a diameter of 160 mum, are better than 80% dense, and manifest the full chi = -1/4 pi shielding in the superconducting state. Temperature-dependent resistivity measurements indicate that MgB2 is a highly conducting metal in the normal state with rho (40 K) = 0.38 mu Omega cm. By using this value, an electronic mean-free path, l approximate to 600 Angstrom can be estimated, indicating that MgB2 wires are well within the clean limit. T-c, H-c2(T), and J(c) data indicate that MgB2 manifests comparable or better superconducting properties in dense wire form than it manifests as a sintered pellet.