Excitonic topological order in imbalanced electron-hole bilayers

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Topological Phases of Matter

Background:

• Correlated systems and frustration are key to novel quantum phases.
• Moat bands in frustrated systems can host topological orders with long-range entanglement.
• Realizing moat-band physics experimentally remains a significant challenge.

Purpose of the Study:

• To explore moat-band phenomena in shallowly inverted InAs/GaSb quantum wells.
• To investigate the behavior of excitonic ground states under imbalanced electron and hole densities.
• To understand the emergence of topological orders in solid-state systems.

Main Methods:

• Experimental investigation of InAs/GaSb quantum wells under varying magnetic fields and density imbalances.
• Observation of bulk gap, edge channels, and Hall signals.
• Theoretical modeling to explain the observed phenomena through excitonic moat bands.

Main Results:

• An unconventional time-reversal-symmetry breaking excitonic ground state was observed.
• A large bulk gap persisted across a broad range of density imbalances at zero magnetic field.
• Edge transport evolved from helical-like to chiral-like with increasing magnetic field, showing a Hall conductance plateau.
• Theoretical analysis confirmed a time-reversal-symmetry breaking excitonic topological order driven by frustration.

Conclusions:

• The study successfully demonstrates moat-band physics in InAs/GaSb quantum wells.
• The observed phenomena are explained by a frustration-induced excitonic topological order.
• This work opens new avenues for researching topological and correlated bosonic systems beyond symmetry-protected topological phases.