<p>The propagation of nonlinear Rayleigh waves in a thermoelastic sandwich structure composed of a thin slab embedded between two identical half-spaces is investigated within the framework of the dual-phase-lag (DPL) thermoelasticity theory. The nonlinearity arises from the temperature dependence of the thermal conductivity. The analysis focuses on an interface-dominated configuration in which the influence of distant external boundaries becomes negligible and the interfacial conditions govern the wave dynamics. The governing equations are solved using the normal mode technique combined with the Poincaré small parameter expansion up to the second-order approximation. Numerical simulations are presented to investigate the influence of the slab thickness on the wave behavior and thermal fields. A comparison between the thin-slab configuration and a three-layer structure with finite outer boundaries is also provided. The results highlight the significant role of interfacial effects in controlling thermal localization, stress distribution, and nonlinear wave propagation in layered thermoelastic structures.</p>