On Dyakonov-Tamm waves localized to a central twist defect in a structurally chiral material

The boundary-value problem of the propagation of Dyakonov-Tamm waves localized to a central twist defect in a structurally chiral material was formulated and numerically solved. The angular magnitude of the twist defect and the orientation of the twist defect relative to the direction of propagation were varied. Detailed analysis showed that either two or three different Dyakonov-Tamm waves can propagate, depending on the angular magnitude and the orientation of the twist defect. These waves have different phase speeds and degrees of localization to the twist-defect interface. The most localized Dyakonov-Tamm waves are essentially confined to within two structural periods of the twist-defect interface on either side.