We investigated the effect of alloying on the upper critical field H c2 for 12 MgB 2 films, in which disorder was introduced by growth, carbon doping or He-ion irradiation, finding a significant H c2 enhancement in C-alloyed films, and an anomalous upward curvature of H c2(T). Record high values of H c2 ⊥(4.2) ≈ 35 T and H c2 ∥(4.2) ≈ 51 T were observed perpendicular and parallel to the ab plane, respectively. The temperature dependence of H c2(T) is described well by a theory of dirty two-gap superconductivity. Extrapolation of the experimental data to T=0 suggests that H c2 ∥(O) may approach the paramagnetic limit of ∼70 T.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Jan 1 2005|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics