Mott insulating phase of strongly interacting two-dimensional excitons.

In condensed-matter physics, electronic Mott insulators have triggered considerable research due to their intricate relation with high-temperature superconductors. However, unlike atomic systems for which Mott phases were recently shown for both bosonic and fermionic species, the fingerprint of a Mott phase implemented with bosons is yet to be found in the solid state. Here we unveil such signature by emulating the Bose-Hubbard hamiltonian with semiconductor excitons confined in a two-dimensional lattice. The exciton fluid is characterised by strong repulsive dipolar interactions. These mostly constrain the system to behave classically, but nevertheless allow for a very narrow parameter space where two Mott phases are formed, with either one or two excitons per lattice site. Our ability to program the lattice geometry explored by excitons then paves the way towards quantum simulations of long-sought many-body phases such as supersolids.