Strongly correlated excitonic insulator in atomic double layers

Area of Science:

• Condensed Matter Physics
• Quantum Many-Body Physics
• Materials Science

Background:

• Excitonic insulators (EIs) are semiconductor phases formed by bound electron-hole pairs (excitons).
• Strong exciton-exciton repulsion is theorized to stabilize condensed phases.
• Conclusive evidence for strongly correlated EI states has been lacking.

Purpose of the Study:

• To demonstrate a strongly correlated two-dimensional (2D) excitonic insulator ground state.
• To provide direct thermodynamic evidence for EI formation.
• To explore the quantum many-boson physics of excitons.

Main Methods:

• Fabrication of transition metal dichalcogenide (TMD) semiconductor double layers.
• Tuning bias voltage to create a quasi-equilibrium spatially indirect exciton fluid.
• Capacitance measurements to probe compressibility and thermodynamic properties.

Main Results:

• Demonstrated a strongly correlated 2D EI ground state.
• Exciton fluid showed exciton-compressibility and charge-incompressibility.
• Measured a dimensionless exciton coupling constant exceeding 10.
• Constructed an exciton phase diagram revealing Mott transition and quasi-condensation.

Conclusions:

• The study provides the first conclusive thermodynamic evidence for strongly correlated excitonic insulator states.
• The findings pave the way for realizing exotic quantum phases of excitons.
• Potential applications in multi-terminal exciton circuitry are suggested.