Plasmon-polaritons on the surface of a pseudosphere
  Plasmon-polariton behavior on the surfaces of constant negative curvature is considered. Analytical solutions for the eigenfrequencies and eigenfunctions are found, which describe resonant behavior of metal nanotips and nanoholes. These resonances may be used to improve performance of metal tips and nanoapertures in various scanning probe microscopy and surface-enhanced spectroscopy techniques. 
Igor I. Smolyaninov, Quirino Balzano, Christopher C. Davis