Topological Switch between Second-Order Topological Insulators and Topological Crystalline Insulators

Area of Science:

• Condensed matter physics
• Materials science
• Quantum mechanics

Background:

• Topological insulators (TIs) exhibit unique electronic properties protected by symmetries.
• Second-order topological insulators (SOTIs) and topological crystalline insulators (TCIs) are distinct phases of matter with unique boundary states.
• SOTIs and TCIs are often protected by mirror and inversion symmetries.

Purpose of the Study:

• To investigate a controllable topological switch between SOTIs and TCIs.
• To explore the role of magnetic fields in inducing topological phase transitions.
• To establish a foundation for novel topological electronic devices.

Main Methods:

• Theoretical investigation of topological phase transitions.
• Definition and calculation of bulk topological numbers.
• Analysis of symmetry protection (mirror and inversion).
• Simulation of edge and corner states under magnetic field influence.

Main Results:

• A topological switch between SOTI and TCI phases was achieved by applying an in-plane magnetic field.
• The system transitions to a TCI when the magnetic field is parallel to helical edges, exhibiting quantized conductance.
• The system transitions to a SOTI when the magnetic field is orthogonal to a diagonal line, revealing topological corner states.
• Achieved a resolution of 10 nm for local magnetization sensing.

Conclusions:

• The study presents a novel method for switching between SOTI and TCI phases using magnetic fields.
• The findings pave the way for developing tunable topological circuits and advanced magnetic sensors.
• The precise control over topological states highlights the potential for future spintronic applications.