  We consider a model of free fermions in a ladder geometry coupled to a
nonuniform cavity mode via Peierls substitution. Since the cavity mode
generates a magnetic field, no-go theorems on spontaneous photon condensation
do not apply, and we indeed observe a phase transition to a photon condensed
phase characterized by finite circulating currents, alternatively referred to
as the equilibrium superradiant phase. We consider both square and triangular
ladder geometries, and characterize the transition by studying the energy
structure of the system, light-matter entanglement, the properties of the
photon mode, and chiral currents. The transition is of first order and
corresponds to a sudden change in the fermionic band structure as well as the
number of its Fermi points. Thanks to the quasi-one dimensional geometry we
scrutinize the accuracy of (mean field) cavity-matter decoupling against large
scale density-matrix renormalization group simulations. We find that
light-matter entanglement is essential for capturing corrections to matter
properties at finite sizes and for the description of the correct photon state.
The latter remains Gaussian in the the thermodynamic limit both in the normal
and photon condensed phases.
