Robust Topological Nodal-Line Semimetals from Periodic Vacancies in Two-Dimensional Materials

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Nodal-line semimetals (NLSMs) are typically sensitive to spin-orbit coupling unless protected by nonsymmorphic symmetries.
• Designing NLSMs often requires searching for materials with specific, complex crystal symmetries.

Purpose of the Study:

• To investigate the possibility of realizing robust NLSMs in two-dimensional (2D) materials by introducing lattice vacancies.
• To demonstrate a novel approach for creating NLSMs by defect engineering in symmorphic crystals.

Main Methods:

• Theoretical investigation using an effective 2D model for borophene.
• Symmetry analysis to identify topological protection mechanisms.
• Simulating the electronic band structure of pristine and defective borophene.

Main Results:

• Spin-orbit coupling and magnetic exchange gap out Dirac cones in pristine borophene.
• Introducing vacancies into borophene leads to the emergence of robust nodal lines (NLs) in the electronic spectrum.
• These nodal lines are topologically protected by a nonsymmorphic glide plane symmetry.

Conclusions:

• Lattice vacancies can be used to engineer robust NLSMs in 2D materials.
• This provides a new paradigm for designing NLSMs by creating defects in ordinary symmorphic crystals, rather than relying on inherently nonsymmorphic materials.