The energy of a two-dimensional neutral particle with a nonzero dipole moment aligned perpendicular to the two-dimensional plane is not controlled by its two-dimensional pseudomomentum, but is a function of a different vector, whereas the particle can gain only two-dimensional pseudomomentum through interaction with the radiation field. A resonance has been found, whose existence derives directly from the above statement.

• Received 30 March 2001

DOI:https://doi.org/10.1103/PhysRevB.66.073306