Momentum-selective graphene spectroscopy of moiré excitons

Abstract

Far-field photoluminescence probes only the light-cone corner of an exciton's momentum content, whereas energy transfer to nearby graphene integrates in-plane momenta up to the inverse spacer thickness $1/z$. For a WSe${}_2$/MoSe${}_2$ heterobilayer we build the transition polarization $\bm{P}_n(\qv)$ of each localized moiré exciton from the registry-dependent vector dipole texture and use each ${\mathbf{P}}_n$ for both baths. The two baths rank the states differently: the graphene-rate ratios differ from the optical ones, their ordering inverts with spacer thickness, and the distance exponents at $z=10$\,nm spread by more than two units. These ratios are independent of the transition-dipole prefactor. Within the $C_3$-symmetric leading-harmonic model the chiral $p_{+}$ and $d_{-}$ states are also dark at normal incidence yet transfer to graphene at rates comparable to the bright ground state. Their graphene rate depends on the sign of the texture phase, a quantity invisible in far-field emission, which we determine from first principles. In a device this prediction requires a splitting, larger than the symmetry-breaking mixing, that protects the chiral partners. Graphene proximity thus acts as a momentum-selective near-field probe of moiré excitons, and we propose its use as a practical spectroscopy.

arXiv comment21 pages, 10 figures