Coulomb-bound four- and five-particle intervalley states in an atomically-thin semiconductor

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Atomically-thin transition metal dichalcogenides (TMDCs) are promising for valleytronics due to their unique optical properties.
• Investigating neutral and charged excitons in TMDCs is well-established, but higher-order correlated quantum states remain elusive.

Purpose of the Study:

• To experimentally demonstrate the existence of four- and five-particle biexcitons and exciton-trions in monolayer tungsten diselenide.
• To characterize the properties and optical signatures of these novel quantum states.

Main Methods:

• Fabrication of high-quality monolayer tungsten diselenide.
• Optical spectroscopy techniques including charge doping, thermal activation, and magnetic-field tuning.

Main Results:

• Experimental evidence for four-particle biexcitons and five-particle exciton-trions is presented.
• Biexcitons and exciton-trions are confirmed to be bound states relative to excitons and trions, respectively.
• These higher-order complexes involve intervalley dark excitons, exhibiting large, negative valley polarization.

Conclusions:

• This work establishes the existence and properties of biexcitons and exciton-trions in TMDCs.
• The findings open new avenues for developing valleytronic quantum devices based on complex TMDC excitations.