  We analyse waves that propagate along the interface between a dielectric
half-space and a half-space filled with a Lorentz material. We show that the
corresponding interface condition leads to a generalisation of the classical
Leontovich condition on the boundary of a dielectric half-space. We study when
this condition supports propagation of (dispersive) surface waves. We derive
the related dispersion relation for waves propagating along the boundary of a
stratified half-space and determine the relationship between the loss
parameter, frequency and wavenumber for which interfacial waves exist.
