Chiral selectivity of unusual helimagnetic transition in iron nanotubes: chirality makes quantum helimagnets.

The remarkable interplay of chirality and magnetism in helical single-wall nanotubes of iron (FeSWNTs) is investigated using fully unconstrained spin-density-functional calculations. Spin-spiral waves exist and noncollinear helimagnetism appears only for the specific chirality of (6,3) and (5,3) FeSWNTs, whereas collinear ferromagnetism persists in other chiral FeSWNTs as unfolded monolayers, that is, chirality selectively involves the unusual helimagnetic phase transition (chiral selectivity). The emergence of quantum helimagnetism plays a variety of significant roles in (i) the stabilization of the chiral FeSWNTs as a long-lived "magic" structure in both freestanding and tip-suspended conditions, (ii) interference with quantum ballistic conductance by interband repulsion, and (iii) the involvement of chiral conductivity in which electric currents pass helically through the FeSWNTs. These chiral characteristics are a novel addition to the intriguing rich diversity of chirality-driven physics and phenomena.