Trends in wavefunction overlap, moiré-patterns and lattice reconstruction studied by interlayer exciton absorption spectroscopy

Interlayer excitons (ILXs), correlated electron-hole pairs split across two vertically stacked semiconducting monolayers, are strongly tunable through electrical field and through twist-angle [1,2,3]. While absorption measurements remain a robust exciton characterization tool, due to the weak oscillator strength of ILXs, to date most ILX characterization has focused on the photoluminescence measurements. Unfortunately, the photoluminescence data can be strongly modified by small strains and defects. Here, we present the ILX absorption spectra for the WSe₂/MoSe₂ heterostructure obtained using an electromodulation technique for samples at different twist-angles and under out-of-plane electric fields. These measurements have allowed us to extract intrinsic radiative lifetimes of ILXs in a robust manner. Looking at their electric field dependence, we obtain a signature of changing electron-hole wavefunction-overlap. In examining the oscillator strength of the ILX for different twist-angles, we find evidence both of a deep moiré potential and of reconstruction of the two materials for small twist angles.

References: [1] A. Jauregui et al., Science 366 (2019). [2] Rivera et al. Nat. Nanotech. (2018) [3] Choi et al. PRL. (2021)