Nonbosonic Moiré Excitons

• Published in: Physical review letters Vol. 132; no. 18; p. 186202
• Main Authors: Huang, Tsung-Sheng, Lunts, Peter, Hafezi, Mohammad
• Format: Journal Article
• Language: English
• Published: United States 03.05.2024
• DOI: 10.1103/PhysRevLett.132.186202

Optical excitations in moiré transition metal dichalcogenide bilayers lead to the creation of excitons, as electron-hole bound states, that are generically considered within a Bose-Hubbard framework. Here, we demonstrate that these composite particles obey an angular momentum commutation relation that is generally nonbosonic. This emergent spin description of excitons indicates a limitation to their occupancy on each site, which is substantial in the weak electron-hole binding regime. The effective exciton theory is accordingly a spin Hamiltonian, which further becomes a Hubbard model of emergent bosons subject to an occupancy constraint after a Holstein-Primakoff transformation. We apply our theory to three commonly studied bilayers (MoSe_{2}/WSe_{2}, WSe_{2}/WS_{2}, and WSe_{2}/MoS_{2}) and show that in the relevant parameter regimes their allowed occupancies never exceed three excitons. Our systematic theory provides guidelines for future research on the many-body physics of moiré excitons.