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

TL;DR

This study explores how carbon doping affects the vortex matter phase diagram in MgB₂, revealing a peak effect below Hc2, changes in pinning behavior, and improved properties for applications.

Contribution

It provides new insights into the vortex phases and pinning phenomena in C-doped MgB₂, highlighting the presence of a peak effect and altered vortex phases.

Findings

Peak effect appears below Hc2 line.

Absence of bulk pinning below H_on(T).

Increased Hc2^c(0) and reduced anisotropy with C doping.

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.