Two-Dimensional Dirac Fermions Protected by Space-Time Inversion Symmetry in Black Phosphorus

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Dirac fermions are exotic quasiparticles with unique electronic properties, crucial for understanding quantum phenomena.
• Two-dimensional (2D) materials offer a unique platform for exploring novel electronic states due to quantum confinement.
• Black phosphorus, a 2D semiconductor, possesses a tunable band gap, making it a promising candidate for advanced electronic applications.

Purpose of the Study:

• To realize and characterize novel symmetry-protected Dirac fermions in a surface-doped 2D semiconductor.
• To investigate the tunability of black phosphorus's band gap using the surface Stark effect.
• To establish black phosphorus as a model system for 2D topological Dirac semimetals.

Main Methods:

• Surface doping of black phosphorus.
• Utilizing the surface Stark effect to tune the band gap.
• High-resolution angle-resolved photoemission spectroscopy (ARPES) for electronic structure analysis.

Main Results:

• Achieved a significant band inversion (up to ~0.6 eV) in black phosphorus.
• Observed the creation and movement of Dirac points along glide-mirror symmetry axes via ARPES.
• Demonstrated the stability of Dirac points, protected by space-time inversion symmetry, even with spin-orbit coupling.

Conclusions:

• Black phosphorus in the inverted regime serves as a robust model system for 2D symmetry-protected Dirac semimetals.
• The stability of its Dirac points distinguishes it from materials like graphene.
• This work opens new avenues for the discovery of 2D Weyl semimetals.