Observation of flat bands in tunable semiconductor artificial graphene*

Flat bands near M points in the Brillouin zone are key features of honeycomb symmetry in artificial graphene (AG) where electrons may condense into novel correlated phases. Here we report the realization of flat bands of AG in GaAs quantum well transistors where the electron density is tuned by applied back-gate voltages. Two new peaks in the low-temperature optical emission spectra are linked to the van-Hove singularity doublet of a pair of flat bands near M-points of AG. As the Fermi level is tuned to overlap the optical emission doublet, PL spectra display dramatic stability against changes in electron density that indicate interplays between key electron-electron interactions and the lattice with honeycomb symmetry [1].
[1] Physical Review Letters, submitted (2020)