  We study the addition of localised impurities to U(N) Supersymmetric
Yang-Mills theories in (p+1)-dimensions by using the gauge/gravity
correspondence. From the gravity side, the impurities are introduced by
considering probe D(8-p)-branes extendingalong the time and radial directions
and wrapping an (7-p)-dimensional submanifold of the internal (8-p)-sphere, so
that the degrees of freedom are point-like from the gauge theory perspective.
We analyse both the configuration in which the branes generate straight flux
tubes -corresponding to actual single impurities - and the one in which
connected flux tubes are created- corresponding to dimers. We discuss the
thermodynamics of both the configurations and the related phase transition. In
particular, the specific heat of the straight flux-tube configuration is
negative for p<3, while it is never the case for the connected one. We study
the stability of the system by looking at the impurity fluctuations. Finally,
we characterise the theory by computing one- and two-point correlators of the
gauge theory operators dual to the impurity fluctuations. Because of the
underlying generalised conformal structure, such correlators can be expressed
in terms of an effective coupling constant (which runs because of its
dimensionality) and a generalised conformal dimension.
