High transport critical currents in dense, metal-clad superconductor wires of MgB2

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In this letter, we report the first successful fabrication of dense, metal-clad MgB2 superconductor wires as well as the first demonstration of high transport Jc of greater than 36,000 A/cm2 in MgB2. The fabrication technique that we devised uses only ambient pressure, yet produces very dense MgB2 with little loss of stoichiometry. Such a technique can be useful for rapid and reliable compound syntheses and characterizations for future discovery of new or improved superconductors with higher Tc, higher Hc2 or improved flux pinning characteristics. We also show that while inherently weak-link-free, the nature of the material is such that the grain boundaries of the polycrystalline MgB2 can easily be altered to exhibit induced weak-link behavior with accompanying loss in critical current density by orders of magnitude.