X-ray Edge Singularities in Nanotubes and Quantum Wires with Multiple Subbands

Band theory predicts a (epsilon - DELTA) sup (-1/2) van Hove singularlity in the tunneling density of states at the minimum energy (DELTA) of an unoccupied subband in a one-dimensional quantum wire. With interactions, an orthogonality catastrophe analogous to the x-ray edge effect for core levels in a metal strongly reduces this singularity to the form (epsilon - DELTA) sup (beta -1/2), with beta ~ 0.3 for typical carbon nanotubes. Despite the anomalous tunneling characteristic, good quasiparticles corresponding to the unoccupied subband states do exist.