Distinguishability of electron-hole pairs and optimality of excitonic complexes in electrostatically-doped semiconductors

To self-consistently explain all observations that are routinely measured in optical studies of charge-tunable semiconductors and to inform on the essential role played by the Pauli exclusion principle, excitonic optical resonances should be classied as being either distinct or indistinct (depending on the distinguishablity of the electron-hole pair), and their underlying excitonic complexes should be classied as being either optimal or suboptimal. A distinguishable e-h pair means that the electron and hole undergoing photoexcitation or recombination have quantum numbers that are not shared by any of the resident carriers. An optimal excitonic complex refers to a complex whose particles come with all available quantum numbers of the resident carriers. Focusing on transition-metaldichalcogenide (TMD) monolayers and their moire heterobilayers, I will show that this classication scheme is a useful framework to understand whether and how various excitonic resonances shift and broaden in energy as the charge density is varied.