Interaction-induced topological insulator states in strained graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Graphene's electronic properties are tunable via mechanical strain.
• Strain induces pseudomagnetic fields, creating flat pseudo-Landau levels (PLLs).
• Understanding many-body effects in strained graphene is crucial for novel electronic states.

Purpose of the Study:

• Investigate the impact of Coulomb interactions on strained graphene with uniform pseudomagnetic fields.
• Explore the emergence of topological states, including quantum Hall and quantum spin-Hall phases.
• Determine the temperature stability and characteristics of these interaction-induced states.

Main Methods:

• Theoretical analysis of Coulomb interactions in strained graphene under a uniform pseudomagnetic field.
• Examination of spin and valley degeneracies of pseudo-Landau levels (PLLs).
• Identification of emergent topological phases at various fractional and integer fillings.

Main Results:

• Coulomb interactions lift spin/valley degeneracies of PLLs, inducing topological insulator states.
• Anomalous quantum Hall states emerge at quarter/three-quarter filling, breaking time-reversal symmetry.
• Time-reversal-symmetric quantum spin-Hall states appear at half-filling, stabilized by spin-orbital interaction.
• Fractional quantum Hall states breaking valley symmetry are observed at fractional fillings.
• These topological states exhibit quantized conductance and persist to hundreds of Kelvin.

Conclusions:

• Coulomb interactions provide a route to engineer robust topological states in strained graphene.
• Strained graphene offers a platform for realizing novel quantum Hall and quantum spin-Hall phenomena.
• These findings pave the way for mesoscopic devices based on topological states in graphene.