Flavor condensate and vacuum (in-)stability in QED2+1

In this letter we study (2+1)-dimensional QED. The first part contains the computation of the flavor symmetry-breaking condensate and its relation to the trace of the energy-momentum tensor, while the second part is concerned with the computation of the effective action allowing for non-constant static external magnetic fields. We do not find that space derivatives in the magnetic field lower the energy of the ground state as compared to a constant field configuration.