Optical Excited States in a Moiré Crystal

• Both intra- and interlayer excitons form in a TMD heterostructure because of the type-II band alignment
• Interlayer excitons are localized in a moiré crystal with a period of ~ 20 nm
• As the twist angle increases, the quantum box (moiré supercell) reduces in size, leading to larger energy spacing between resonances
• The optical selection rules are spatially dependent as shown theoretically
• Multiple interlayer excitons are observed with alternating circular emission
• First evidence of localized excitons in a moiré crystal
• Potential applications as a regular array of quantum dots as single photon emitters

Technical Description of Work: In transition metal dichalcogenides (TMDC) monolayers, there are two inequivalent valleys (energy extrema points in the band structure) related by time-reversal symmetry. Fundamental optical excitations, or excitons (bound electron-hole pairs) are formed at these valleys. The large spin orbit interaction in these materials leads to large energy splitting between the spin up and down states and valley contrasting optical selection rules. To utilize valley as a new information carrier, a simple method to separate this degree of freedom at room temperature is required.