Quantum Heisenberg spin chains in reconstructed armchair graphene nanoribbons towards ballistic quantum spin transport

It is well-known that ferromagnetism can be realized along a pristine zigzag graphene nanoribbon edge (ZGNE), but the pristine armchair graphene nanoribbon edge (AGNE) is nonmagnetic. Here, we achieve Heisenberg antiferromagnetic (AFM) spin chains through reconstruction of the AGNEs. The reconstructed edge consists of pentagonal carbon rings or a hybrid of pentagonal and hexagonal carbon rings, and its total energy per carbon atom (indicating stability) is between those of AGNE and ZGNE. The resultant nanoribbons are narrow-gap semiconductors and their band-edge states are either nonmagnetic bulk states or spin-degenerate real-space edge states due to the reconstructed edges. The spin is located on the outermost carbon of the pentagonal ring, and the inter-spin exchange is the nearest-neighbor AFM interaction. For finite chain length or nonzero magnetization, there are nonzero spin Drude weights and thus ballistic quantum spin transport can be achieved along the reconstructed edges. These could be useful for graphene-related quantum spin information and spintronics applications.