Stacking-induced type-II quantum spin Hall insulators with high spin Chern number in unconventional magnetism

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Stacking type-I quantum spin Hall insulators typically results in a trivial insulator.
• The behavior of stacked type-II quantum spin Hall insulators is not well understood.

Purpose of the Study:

• Investigate the properties of stacked type-II quantum spin Hall insulators.
• Explore the potential for novel topological phases and enhanced spin Hall conductivity.

Main Methods:

• Lattice model calculations.
• First-principles electronic structure calculations.
• Analysis of spin Chern number and edge states.

Main Results:

• Stacking two type-II quantum spin Hall insulators forms a nontrivial phase with a high spin Chern number.
• The bilayer exhibits two pairs of topological edge states with opposite chirality and polarization.
• Quantized spin Hall conductivity is doubled compared to the monolayer.
• The phase is stable under U(1) symmetry and robust to its breaking.
• Bilayer Nb2SeTeO is identified as a type-II quantum spin Hall insulator with a high spin Chern number.

Conclusions:

• Stacking type-II quantum spin Hall insulators leads to a distinct topological phase compared to type-I.
• This work provides a pathway to achieve highly quantized spin Hall conductivity.
• The findings deepen the understanding of type-I versus type-II quantum spin Hall insulators.