  Recent studies have shown that the large-scale gas dynamics of protoplanetary
disks (PPDs) are controlled by non-ideal magneto-hydrodynamics (MHD), but how
this influences dust dynamics is not fully understood. To this end, we
investigate the stability of dusty, magnetized disks subject to the Hall
effect, which applies to planet-forming regions of PPDs. We find a novel
Background Drift Hall Instability (BDHI) that may facilitate planetesimal
formation in Hall-effected disk regions. Through a combination of linear
analysis and nonlinear simulations, we demonstrate the viability and
characteristics of BDHI. We find it can potentially dominate over the classical
streaming instability (SI) and standard MHD instabilities at low dust-to-gas
ratios and weak magnetic fields. We also identify magnetized versions of the
classic SI, but these are usually subdominant. We highlight the complex
interplay between magnetic fields and dust-gas dynamics in PPDs, underscoring
the need to consider non-ideal MHD like the Hall effect in the broader
narrative of planet formation.
