Effect of axial torsion on sp carbon atomic wires.

Ab initio calculations within density-functional theory combined with experimental Raman spectra on cluster-beam deposited pure-carbon films provide a consistent picture of sp-carbon chains stabilized by sp;{3} or sp;{2} terminations, the latter being sensitive to torsional strain. This unexplored effect promises many exciting applications since it allows one to modify the conductive states near the Fermi level and to switch on and off the on-chain pi-electron magnetism.