PHASON MODES IN A SPIN-DENSITY-WAVE IN THE PRESENCE OF LONG-RANGE COULOMB INTERACTION

We study the effect of long-range Coulomb interaction on the phason in spin-density waves (SDW's) within mean-field theory. In the longitudi nal limit and in the absence of SDW pinning, the phason is completely absorbed by the plasmon due to the Anderson-Higgs mechanism. In the pr esence of SDW pinning or when the wave vector q is tilted from the cha in direction, though the plasmon still almost exhausts the optical sum rule, another optical mode appears at omega < 2DELTA(T), with small o ptical weight. This low-frequency mode below the SDW gap may be access ible to electron-energy-loss spectroscopy.