Band splitting for Si(557)-Au: Is it spin-charge separation?

It has been proposed that the Si(557)-Au surface exhibits spin-charge separ ation in a one-dimensional electron liquid. Two narrowly spaced bands are f ound which exhibit a well-defined splitting at the Fermi level. That is inc ompatible with the assignment to a spinon-holon pair in a Luttinger liquid. instead, we propose that the two bands are associated with two nearly dege nerate atomic chains, or a chain of step atoms with two broken bonds. Such an assignment explains why the surface is metallic despite an even number o f electrons per unit cell.