Bogoliubov quasiparticles, spinons, and spin-charge decoupling in superconductors

We show that, in the presence of Coulomb interactions, the charge of a quasiparticle in a fully gapped superconductor is a sharp quantum observable. It follows that the familiar Bogoliubov quasiparticles are neutral, spin-1/2 fermions. Since the current-carrying collective modes are spinless, charge and spin are carried by separate excitations in a superconductor. The quantum numbers of these quasiparticles are identical to those of a spinon in a ``resonating-valence-bond'' (RVB) superconductor. This supports the notion that a RVB superconductor is simply a strong-coupling version of a BCS superconductor. We describe an experiment that would directly verify the separation of charge and spin in a bulk superconductor.