CT-invariant quantum spin Hall effect in ferromagnetic graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• The quantum spin Hall effect (QSHE) is typically protected by time-reversal (T) invariance.
• Existing QSHE models rely on spin-orbit interaction for their physical origin.
• Ferromagnetic materials offer alternative platforms for exploring novel quantum effects.

Purpose of the Study:

• To predict a novel quantum spin Hall effect (QSHE) in ferromagnetic graphene.
• To investigate the physical origin and protective symmetries of this new QSHE.
• To analyze the resulting longitudinal and spin Hall resistance characteristics.

Main Methods:

• Theoretical prediction of QSHE in ferromagnetic graphene under a magnetic field.
• Analysis of symmetry protection, identifying CT invariance (Charge conjugation-Time reversal).
• Calculation of longitudinal resistance quantum plateaus and spin Hall resistance.

Main Results:

• A novel QSHE is predicted in ferromagnetic graphene, independent of spin-orbit interaction.
• This QSHE is protected by CT invariance, differing from T-invariant QSHE.
• Longitudinal resistance exhibits quantum plateaus at specific fractional values (1/2, 1/6, 3/28, ...), dependent on carrier filling.
• The spin Hall resistance is found to be robust against disorder.

Conclusions:

• Ferromagnetic graphene provides a new avenue for realizing QSHE without spin-orbit interaction.
• The CT invariance protection mechanism offers a distinct pathway for topological phenomena.
• The predicted quantum plateaus and robust spin Hall resistance highlight potential applications in spintronics.