Experimental measurement of the intrinsic excitonic wavefunction

TL;DR

This study directly images the excitonic wavefunction in reciprocal space and visualizes electron distribution around the hole in monolayer WSe2, confirming theoretical predictions about energy-momentum dispersion.

Contribution

It presents the first direct measurement of the excitonic wavefunction in reciprocal space and visualizes the real-space electron distribution in a 2D material.

Findings

Direct imaging of excitonic wavefunction achieved.

Visualization of electron distribution around the hole.

Confirmation of inverted energy-momentum dispersion prediction.

Abstract

An exciton, a two-body composite quasiparticle formed of an electron and hole, is a fundamental optical excitation in condensed-matter systems. Since its discovery nearly a century ago, a measurement of the excitonic wavefunction has remained beyond experimental reach. Here, we directly image the excitonic wavefunction in reciprocal space by measuring the momentum distribution of electrons photoemitted from excitons in monolayer WSe2. By transforming to real space, we obtain a visual of the distribution of the electron around the hole in an exciton. Further, by also resolving the energy coordinate, we confirm the elusive theoretical prediction that the photoemitted electron exhibits an inverted energy-momentum dispersion relationship reflecting the valence band where the partner hole remains, rather than that of conduction-band states of the electron.