  We investigate the propagation of surface plasmons (SPPs) in a thin layer of
copper surrounded by copper oxide Cu$_2$O. It is shown that particularly strong
excitons in Cu$_2$O can have considerable impact on plasmon propagation,
providing many opportunities for plasmon-exciton and plasmon-plasmon
interactions. It is demonstrated that by the use of sufficiently thin metal
layer, one can excite the so-called long range plasmons (LRSPPs) which can
overcome the inherently high ohmic losses of Cu as compared to usual plasmonic
metals such as silver. Analytical results are confirmed by numerical
calculations.
