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Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering
Gurevich, A.; Patnaik, S.; Braccini, V.; Kim, K. H.; Mielke, C.; Song, X.; Cooley, L. D.; Bu, S. D.; Kim, D. M.; Choi, J. -H.; Belenky, L. J.; Giencke, J.; Lee, M. K.; Tian, W.; Pan, X. Q.; Siri, A.; Hellstrom, E. E.; Eom, C. B.; Larbalestier, D. C.
2004-02-01
Citation:Gurevich, A; Patnaik, S; Braccini, V; Kim, K H; Mielke, C; Song, X; Cooley, L D; Bu, S D; Kim, D M; Choi, J H; Belenky, L J; Giencke, J; Lee, M K; Tian, W; Pan, X Q; Siri, A; Hellstrom, E E; Eom, C B; Larbalestier, D C (2004). "Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering." Superconductor Science and Technology. 17(2): 278-286. <http://hdl.handle.net/2027.42/48993>
Abstract: We report a significant enhancement of the upper critical field Hc2 of different MgB2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities ρ, we show a clear trend of an increase in Hc2 as ρ increases. One particular high resistivity film had a zero-temperature Hc2(0) well above the Hc2 values of competing non-cuprate superconductors such as Nb3Sn and Nb–Ti. Our high-field transport measurements give record values T and T for high resistivity films and T for untextured bulk polycrystals. The highest Hc2 film also exhibits a significant upward curvature of Hc2(T) and a temperature dependence of the anisotropy parameter opposite to that of single crystals: γ(T) decreases as the temperature decreases, from to . This remarkable Hc2 enhancement and its anomalous temperature dependence are a consequence of the two-gap superconductivity in MgB2, which offers special opportunities for further Hc2 increases by tuning of the impurity scattering by selective alloying on Mg and B sites. Our experimental results can be explained by a theory of two-gap superconductivity in the dirty limit. The very high values of Hc2(T) observed suggest that MgB2 can be made into a versatile, competitive high-field superconductor.
