Superconductivity in dense MgB2 wires

MgB2 becomes superconducting just below 40 K. Whereas porous polycrystallin e 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 fila ments to Mg vapor. The resulting wires have a diameter of 160 mum, are bett er than 80% dense, and manifest the full chi = -1/4 pi shielding in the sup erconducting 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 a pproximate 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 MgB 2 manifests comparable or better superconducting properties in dense wire f orm than it manifests as a sintered pellet.