  We have studied spectral properties of a cholesteric liquid crystal with a
combined defect consisting of a nanocomposite layer and a twist. The
nanocomposite layer is made of metallic nanoballs dispersed in a transparent
matrix and featuring effective resonant permittivity. A solution has been found
for the transmission spectrum of circularly polarized waves in the structure.
We have analyzed spectral splitting of the defect mode in the bandgap of the
cholesteric when its frequency coincides with the nanocomposite resonant
frequency. Defect modes have characteristics strongly dependent on the
magnitude and direction of the phase jump at the interface between
nanocomposite and cholesteric layers. It has been found that the bandgap width
and the position and localization degree of defect modes can be effectively
controlled by external fields applied to cholesteric.
