Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering. Gurevich, A, Patnaik, S, Braccini, V, Kim, K., Mielke, C, Song, X, Cooley, L., Bu, S., Kim, D., Choi, J., Belenky, L., Giencke, J, Lee, M., Tian, W, Pan, X., Siri, A, Hellstrom, E., Eom, C., & Larbalestier, D. SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 17(2, S):278-286, FEB, 2004.
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We report a significant enhancement of the upper critical field H-c2 of different MgB2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities rho, we show a clear trend of an increase in H-c2 as rho increases. One particular high resistivity film had a zero-temperature H-c2(0) well above the H-c2 values of competing non-cuprate superconductors such as Nb3Sn and Nb-Ti. Our high-field transport measurements give record values H-c2(perpendicular to) (0) approximate to34 T and H-c2(parallel to) (0) approximate to49 T for high resistivity films and H-c2(0) approximate to 29 T for untextured bulk polycrystals. The highest H-c2 film also exhibits a significant upward curvature of H-c2 (T) and a temperature dependence of the anisotropy parameter gamma (T) = H-c2(parallel to)/H-c2(perpendicular to) opposite to that of single crystals: gamma (T) decreases as the temperature decreases, from gamma (T-c) approximate to 2 to gamma (0) approximate to 1.5. This remarkable H-c2 enhancement and its anomalous temperature dependence are a consequence of the two-gap superconductivity in MgB2, which offers special opportunities for further H-c2 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 H-c2(T) observed suggest that MgB2 can be made into a versatile, competitive high-field superconductor.
@article{ ISI:000189103100028,
Author = {Gurevich, A and Patnaik, S and Braccini, V and Kim, KH and Mielke, C and
   Song, X and Cooley, LD and Bu, SD and Kim, DM and Choi, JH and Belenky,
   LJ and Giencke, J and Lee, MK and Tian, W and Pan, XQ and Siri, A and
   Hellstrom, EE and Eom, CB and Larbalestier, DC},
Title = {{Very high upper critical fields in MgB2 produced by selective tuning of
   impurity scattering}},
Journal = {{SUPERCONDUCTOR SCIENCE \& TECHNOLOGY}},
Year = {{2004}},
Volume = {{17}},
Number = {{2, S}},
Pages = {{278-286}},
Month = {{FEB}},
Abstract = {{We report a significant enhancement of the upper critical field H-c2 of
   different MgB2 samples alloyed with nonmagnetic impurities. By studying
   films and bulk polycrystals with different resistivities rho, we show a
   clear trend of an increase in H-c2 as rho increases. One particular high
   resistivity film had a zero-temperature H-c2(0) well above the H-c2
   values of competing non-cuprate superconductors such as Nb3Sn and Nb-Ti.
   Our high-field transport measurements give record values
   H-c2(perpendicular to) (0) approximate to34 T and H-c2(parallel to) (0)
   approximate to49 T for high resistivity films and H-c2(0) approximate to
   29 T for untextured bulk polycrystals. The highest H-c2 film also
   exhibits a significant upward curvature of H-c2 (T) and a temperature
   dependence of the anisotropy parameter gamma (T) = H-c2(parallel
   to)/H-c2(perpendicular to) opposite to that of single crystals: gamma
   (T) decreases as the temperature decreases, from gamma (T-c) approximate
   to 2 to gamma (0) approximate to 1.5. This remarkable H-c2 enhancement
   and its anomalous temperature dependence are a consequence of the
   two-gap superconductivity in MgB2, which offers special opportunities
   for further H-c2 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 H-c2(T) observed suggest that MgB2 can be made
   into a versatile, competitive high-field superconductor.}},
DOI = {{10.1088/0953-2048/17/2/008}},
Article-Number = {{PII S0953-2048(04)68338-2}},
ISSN = {{0953-2048}},
ResearcherID-Numbers = {{Cooley, Lance/E-7377-2015
   Gurevich, Alex/A-4327-2008
   Bu, Sang Don/B-1576-2008
   Eom, Chang-Beom/I-5567-2014
   Larbalestier, David/B-2277-2008}},
ORCID-Numbers = {{Cooley, Lance/0000-0003-3488-2980
   Gurevich, Alex/0000-0003-0759-8941
   Bu, Sang Don/0000-0003-4883-1308
   Larbalestier, David/0000-0001-7098-7208}},
Unique-ID = {{ISI:000189103100028}},
}
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