Photoemission spectra of massless Dirac fermions on the verge of exciton condensation

Angle-resolved photoemission spectroscopy (ARPES) is a powerful probe of electron correlations in two-dimensional layered materials. In this article we demonstrate that ARPES can be used to probe the onset of exciton condensation in spatially separated systems of electrons and holes created by gating techniques in either double-layer graphene or topological-insulator thin films.