Recent progress on topological semimetal IrO₂: electronic structures, synthesis, and transport properties

Area of Science:

• Condensed matter physics
• Materials science
• Solid-state physics

Background:

• 5d transition metal oxides, particularly iridates, are of significant interest due to strong spin-orbit coupling (SOC).
• Iridium dioxide (IrO2), a known catalyst, exhibits novel topological states and exotic transport properties.
• The interplay of strong SOC and nonsymmorphic symmetry in IrO2 leads to symmetry-protected Dirac nodal lines (DNLs) and a large spin Hall effect.

Purpose of the Study:

• To review recent advances in the study of iridium dioxide (IrO2).
• To emphasize understanding its topological electronic structures, synthesis of nanostructures, and fundamental transport properties.
• To discuss the theoretical origin and implications of DNLs and the spin Hall effect in IrO2.

Main Methods:

• Theoretical analysis of band structure and symmetry protection.
• Synthesis of high-quality IrO2 nanostructures (thin films, nanowires).
• Experimental measurements of electrical, spin, and thermal transport properties.

Main Results:

• Identification of fourfold degenerate DNLs in IrO2's band structure.
• Demonstration of a large spin Hall effect in IrO2.
• Observation that transport properties are sensitive to strain, dimensionality, quantum confinement, film texture, and disorder.

Conclusions:

• IrO2 is a unique SOC oxide with tunable transport properties.
• Competing energy scales (SOC, disorder, etc.) enable intriguing quantum states.
• Further research on IrO2 nanostructures holds promise for novel quantum phenomena.