Spectroscopic signatures of excitonic order on quantum spin Hall edge states

One of the proposed ground states of monolayer ${\mathrm{WTe}}_{2}$, a two-dimensional topological insulator, is an excitonic condensate. However, time-reversal preserving and breaking solutions are competing at the mean-field level of analysis, and it is unclear which condensate, if any, is realized in nature. In this work we analyze the experimental signatures that allow to provide evidence for the excitonic ground states and to distinguish between the two types of condensates using scanning tunneling microscopy. We provide clear experimental signatures in local mapping and quasiparticle interference patterns that visualize the expected changes in local charge and spin density, and characterize allowed backscattering processes in the presence of impurities and disorder. Our results will thus help in the determination of the nature of the ${\mathrm{WTe}}_{2}$ ground state.