Point defects in two-dimensional RuCl3

Defects are crucial in determining a variety of material properties especially in low dimensions. In this work, we study point defects in monolayer α-phase Ruthenium (III) chloride (α-RuCl3), a promising candidate to realize quantum spin liquid with nearly degenerate magnetic states. Our first-principles simulations reveal that Cl vacancies, Ru vacancies, and oxygen substitutional defects are the most energetically stable point defects. Besides, these point defects break the magnetic degeneracy: Cl vacancies and oxygen substitutional defects energetically favor the zigzag-antiferromagnetic configuration while Ru vacancies favor the ferromagnetic configuration, shedding light on understanding the observed magnetic structures and further defect engineering of magnetism in monolayer α-RuCl3. We further calculated their electronic structures and optical absorption spectra. The polarization symmetry of optical responses provides a convenient signature to identify the point defect types and long-range magnetic orders.