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.
@article{arxiv.2011.13104,
title = {Experimental measurement of the intrinsic excitonic wavefunction},
author = {Michael K. L. Man and Julien Madéo and Chakradhar Sahoo and Kaichen Xie and Marshall Campbell and Vivek Pareek and Arka Karmakar and E Laine Wong and Abdullah Al-Mahboob and Nicholas S. Chan and David R. Bacon and Xing Zhu and Mohamed Abdelrasoul and Xiaoquin Li and Tony F. Heinz and Felipe H. da Jornada and Ting Cao and Keshav M. Dani},
journal= {arXiv preprint arXiv:2011.13104},
year = {2020}
}