Dual-density waves with neutral and charged dipolar excitons of GaAs bilayers.

Strongly correlated quantum particles in lattice potentials are the building blocks for a wide variety of quantum insulators-for instance, Mott phases and density waves breaking lattice symmetry 1-3 . Such collective states are accessible to bosonic and fermionic systems 2,4-10,11,12 . To expand further the spectrum of accessible quantum matter phases, mixing both species is theoretically appealing because density order then competes with phase separation 13-16 . Here we manipulate such a Bose-Fermi mixture by confining neutral (boson-like) and charged (fermion-like) dipolar excitons in an artificial square lattice of a GaAs bilayer. At unitary lattice filling, strong inter- and intraspecies interactions stabilize insulating phases when the fraction of charged excitons is around (1/3, 1/2, 2/3). We evidence that dual Bose-Fermi density waves are then realized, with species ordered in alternating stripes. Our observations highlight that dipolar excitons allow for controlled implementations of Bose-Fermi Hubbard models extended by off-site interactions.