Polarization-Induced Phase Transitions in Ultra-Thin InGaN-Based Double Quantum Wells

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Topological insulators (TIs) are materials with unique electronic properties, offering potential for advanced electronic devices.
• Indium Gallium Nitride (InGaN) based nanostructures are promising for exploring TI properties due to tunable band structures.
• Understanding phase transitions in these heterostructures is crucial for their practical application.

Purpose of the Study:

• To investigate the conditions for achieving topological insulator phases in InGaN/GaN and InN/InGaN double quantum wells.
• To analyze the influence of quantum well and barrier widths on phase transitions.
• To identify novel phase transitions and their characteristics in these nanostructures.

Main Methods:

• Utilized a realistic model combining nonlinear elasticity, piezoelectricity, and the eight-band k·p method.
• Incorporated relativistic and nonrelativistic linear-wave-vector terms, including a negative effective spin-orbit interaction in InN.
• Simulated phase transitions including normal insulator, topological insulator, Weyl semimetal, and nonlocal semimetal phases.

Main Results:

• Demonstrated the possibility of topological insulator phases in InGaN/GaN and InN/InGaN double quantum wells with specific monolayer (ML) widths (e.g., 2/3 MLs, 3/3 MLs).
• Observed topological phase transitions from normal insulator to TI via Weyl semimetal, and nontopological transitions to nonlocal topological semimetal with thin interwell barriers.
• Identified that the topological insulator phase deteriorates with increasing interwell barrier width, with novel transitions occurring at wider barriers.

Conclusions:

• Achieving topological insulator states in InGaN-based double quantum wells is feasible under optimized structural parameters.
• The interwell barrier width critically affects the stability and existence of the topological insulator phase.
• The findings provide a roadmap for designing and fabricating InGaN nanostructures for topological electronic applications.