Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effect of doping on irreversible Campbell length in MgB$_2$ single
  crystals   We have measured small-amplitude rf penetration depth $\lambda(H,T)$ in pure
and C, Li and (Li+C) doped single crystals of MgB$_2$. The effect of doping on
the critical temperature T$_c$ and on the upper critical field H$_{c2}$ was
found to be in good agreement with previous results. We report the presence of
clear signatures of irreversibility in $\lambda(H,T)$, associated with the peak
effect. Carbon doping enhances the signature and shifts its position on the H-T
phase diagram to higher temperatures. Contrary to this, Li substitution has the
effect of suppressing the peak effect to lower temperatures. Analysis of both
zero field (ZFC) and field cooled (FC) measurements suggests that the
hysteresis associated with the peak effect is due to macroscopic screening
supercurrents, $j$, generated during the magnetic field ramp.

21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs