A Gurevich et al 2004 Supercond. Sci. Technol. 17 278 doi:10.1088/0953-2048/17/2/008
Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering
A Gurevich1, S Patnaik1,5, V Braccini1,3, K H Kim2, C Mielke2, X Song1, L D Cooley1,6, S D Bu1, D M Kim1, J H Choi1, L J Belenky1, J Giencke1, M K Lee1, W Tian4, X Q Pan4, A Siri3, E E Hellstrom1, C B Eom1 and D C Larbalestier1
Show affiliationsWe 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.
- PACS
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Fy Transport properties (electric and thermal conductivity, thermoelectric effects, etc.)
- Subjects
- Dates
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Issue 2 (February 2004)
Received 28 August 2003, in final form 19 November 2003
Published 19 December 2003
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Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering
A Gurevich et al 2004 Supercond. Sci. Technol. 17 278
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