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Influence of carbon doping in the vortex matter properties of MgB$_2$

M. Pissas·D. Stamopoulos·S. Lee·S. Tajima
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Abstract

We have studied the vortex-matter phase diagram of low C doped MgB$_2$ superconductor. The significant finding is the appearance of a peak effect, which, as both our global magnetization and local ac susceptibility measurements revealed, is placed well below the $H_{c2}$-line. The absence of significant bulk pinning below the onset line $H_{on}(T)$ of the peak effect implies that the Bragg glass phase is present for $H < H_{on}(T)$. Interestingly, the unexpected absence of bulk pinning above the end point line $H_{ep}(T)$ of the peak effect implies the presence of a slightly pinned vortex phase in the regime $H_{ep}(T) < H < H_{c2}(T)$. In addition, the observed increase of the $H_{c2}^c(0)$ since the carbon doped MgB$_2$ becomes more dirty and the reduced anisotropy, in comparison to the pure MgB$_2$, makes the C-doped MgB$_2$ more favorable for practical applications.

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M. Pissas, D. Stamopoulos, S. Lee, S. Tajima. 2003-12-14. Influence of carbon doping in the vortex matter properties of MgB$_2$. https://arxiv.org/abs/cond-mat/0312350

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