  In the framework of Berthelot's theory of arithmetic $\mathcal{D}$-modules,
we introduce the notion of arithmetic $\mathcal{D}$-modules having
potentially-unipotent monodromy. For example, from Kedlaya's semistable
reduction theorem, overconvergent isocrystals with Frobenius structure have
potentially unipotent monodromy. We construct some coefficients stable under
Grothendieck's six operation, containing overconvergent isocrystals with
Frobenius structure and whose object have potentially unipotent monodromy.
  On the other hand, we introduce the notion of arithmetic
$\mathcal{D}$-modules having quasi-unipotent monodromy. These objects are
overholonomic, contain the isocrystals having potentially unipotent monodromy
and are stable under Grothendieck's six operations and under base change.
