We develop a variational framework to detect high energy
solutions of the planar Schrödinger–Poisson system
with a positive function
a∈L∞(R2) and
γ>0. In particular, we deal with the periodic setting where the corresponding functional is invariant under
Z2-translations and therefore fails to satisfy a global Palais–Smale condition. The key tool is a surprisingly strong compactness condition for Cerami sequences which is not available for the corresponding problem in higher space dimensions. In the case where the external potential
a is a positive constant, we also derive, as a special case of a more general result, the existence of
nonradial solutions (u,w) such that
u has arbitrarily many nodal domains. Finally, in the case where
a is constant, we also show that
solutions of the above problem with
u>0 in
R2 and
w(x)→−∞ as
|x|→∞ are radially symmetric up to translation. Our results are also valid for a variant of the above system containing a local nonlinear term in
u in the first equation.