Interacting multi-channel topological boundary modes in a quantum Hall valley system

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Quantum Hall ferromagnets (QHFMs) are 2D electronic phases with broken symmetry and topological properties.
• Domain walls between QHFM phases are predicted to host gapless 1D modes due to topological changes.
• Interacting electronic modes at these domain walls have remained experimentally unprobed.

Purpose of the Study:

• To directly visualize spontaneous boundary modes at QHFM domain walls.
• To investigate the nature of these modes, particularly their interaction and topological properties.
• To explore the tunability of these modes by controlling valley polarization and flavor.

Main Methods:

• Utilized scanning tunneling microscopy (STM) to image domain walls in bismuth.
• Employed spectroscopy to probe the electronic properties of the boundary modes.
• Manipulated valley polarization and the number of modes to study interaction effects.

Main Results:

• Successfully visualized boundary modes at domain walls between QHFM phases with different valley polarization.
• Observed that these modes exist within a topological energy gap that closes and reopens with polarization switching.
• Demonstrated that valley-polarized channels can be tuned to be metallic or develop a spectroscopic gap due to Coulomb interactions.

Conclusions:

• The study provides direct visualization and characterization of interacting 1D quantum channels at QHFM domain walls.
• The observed tunable behavior highlights the role of Coulomb interactions and valley flavor in these topological modes.
• QHFM domain walls in various 2D materials offer a platform for exploring rich interaction physics in quantum wires.