Neutral and charged inter-valley biexcitons in monolayer MoSe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Atomically thin transition metal dichalcogenides (TMDs) exhibit strong Coulomb interactions due to reduced dielectric screening.
• Excitons and trions dominate optical properties, but higher-order states like biexcitons are challenging to identify.
• Linear optical spectroscopy struggles to unambiguously resolve complex many-body states in TMDs.

Purpose of the Study:

• To implement polarization-resolved two-dimensional coherent spectroscopy (2DCS) for unraveling the optical response of monolayer MoSe2.
• To identify and characterize higher-order correlated optical states, specifically biexcitons.
• To explore the potential of inter-valley biexcitons for novel optoelectronic applications.

Main Methods:

• Utilized polarization-resolved two-dimensional coherent spectroscopy (2DCS).
• Analyzed monolayer MoSe2 to probe its complex optical response.
• Developed a theoretical model incorporating valley-dependent optical selection rules.

Main Results:

• Identified distinct resonances corresponding to neutral and charged inter-valley biexcitons in cross-polarized 2D spectra.
• Determined binding energies of ~20 meV for neutral and ~5 meV for charged inter-valley biexcitons.
• The theoretical model elucidated the quantum pathways responsible for these biexciton states.

Conclusions:

• Inter-valley biexcitons, composed of excitons from different valleys, have been unambiguously identified in monolayer MoSe2.
• These findings provide crucial insights into many-body physics in low-dimensional materials.
• The identified biexcitons offer promising avenues for developing ultrathin biexciton lasers and polarization-entangled photon sources.