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Anisotropies of the lower and upper critical fields in MgB$_2$ single crystals

L. Lyard·P. Szabo·T. Klein·J. Marcus·C. Marcenat·B. W. Kang·K. H. Kim·H. S. Lee·S. I. Lee
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Abstract

The temperature dependence of the London penetration depth ($λ$) and coherence length ($ξ$) has been deduced from Hall probe magnetization measurements in high quality MgB$_2$ single crystals in the two main crystallographic directions. We show that, in contrast to conventional superconductors, MgB$_2$ is characterized by two different anisotropy parameters ($Γ_λ= λ_c/λ_{ab}$ and $Γ_ξ= ξ_{ab}/ξ_c$) which strongly differ at low temperature and merge at $T_c $. These results are in very good agreement with recent calculations in weakly coupled two bands suprerconductors (Phys. Rev. B, 66, 020509(R) (2002).

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L. Lyard, P. Szabo, T. Klein, J. Marcus, C. Marcenat, B. W. Kang, K. H. Kim, H. S. Lee, S. I. Lee. 2003-07-16. Anisotropies of the lower and upper critical fields in MgB$_2$ single crystals. https://doi.org/10.1103/physrevlett.92.057001

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