Supersymmetry has led to profound discoveries in Quantum Field Theory, providing analytic control at strong coupling and revealing new dualities for gauge theories. In this seminar we argue that it is possible to preserve supersymmetry also at finite density, and discuss its implications for the dynamics of (2+1)-dimensional systems. We will analyze the case of 3d QED with eight supercharges, doped by various configurations of electric charges or magnetic fluxes. The strong coupling limit admits a dual description in terms of a free theory. At finite density, the duality relates electric and magnetic configurations, and allows to find backreacted solutions for arbitrary lattices of defects in the infrared.