The extraordinary superconductivity of commercial niobium-titanium wire at extreme pressures

We report the observation of extraordinary superconductivity in a pressurized commercial niobium-titanium alloy wire. We demonstrate that its zero-resistance superconductivity persists from ambient pressure to pressures as high as 261.7 GPa, a pressure that falls within that of the outer core of the earth, establishing the record where a superconducting state continuously survives. At such high pressures the superconducting transition temperature (T_C) has increased from ~9.6 K to ~19.1 K and the critical magnetic field (H_C2) at 1.8 K from 15.4 T to 19 T, setting new records for both T_C and H_C2 among all the known transition element alloy superconductors, all, remarkably, in spite of a 45% volume shrinkage. The behavior is quite different from what is seen in copper oxide and iron pnictide superconductors, whose superconducting transition temperatures are quite sensitive to subtle changes in the lattice structure. Our results therefore not only provide fresh information on the remarkable properties of this commercial superconductor, but also pose a substantial challenge for models of a phenomenon as “well understood” as conventional electron-phonon coupled superconductivity.