  As the electron in the hydrogen atom, a bosonic field can bind itself to a
black hole occupying a discrete infinite set of states. When (i) the spacetime
is prone to superradiance and (ii) a confinement mechanism is present, some of
such states are infinitely long-lived. These equilibrium configurations, known
as stationary clouds, are states "synchronized" with a rotating black hole's
event horizon. For most, if not all, stationary clouds studied in the
literature so far, the requirements (i)-(ii) are independent of each other.
However, this is not always the case. This paper shows that massless neutral
scalar fields can form stationary clouds around a Reissner-Nordstr\"{o}m black
hole when both are subject to a uniform magnetic field. The latter
simultaneously enacts both requirements by creating an ergoregion (thereby
opening up the possibility of superradiance) and trapping the scalar field in
the black hole's vicinity. This leads to some novel features, in particular,
that only black holes with a subset of the possible charge to mass ratios can
support stationary clouds.
