Magnetic instability in the spin susceptibility of chiral carbon-based structures

Chiral carbon nanostructures have been found to display unexpected magnetic behaviors. Several theoretical calculations performed in the macroscopic limit q=0 have addressed or predicted some of these findings. To gain more insight into the magnetism of these systems at finite q, here we use linear response theory to calculate the wave-vector-dependent spin susceptibility χ(q,0) in a half-filling tight-binding model of a helix of carbon atoms with intrinsic spin-orbit coupling (SOC). We find that at the nesting wave number q=2kF the paramagnetic state of the system is unstable with respect to the formation of a spin-density-wave type state. Chirality has a small effect on the paramagnetic phase but has no impact on the spin-density-wave type state.