  Spinodal decomposition is proposed for stabilizing self-assembled interfaces
between topological insulators (TIs) by combining layers of iso-structural and
iso-valent TlBi$X_2$ ($X$=S, Se, Te) materials. The composition range for
gapless states is addressed concurrently to the study of thermodynamically
driven boundaries. By tailoring composition, the TlBiS$_2$-TlBiTe$_2$ system
might produce both spinodal superlattices and two dimensional eutectic
microstructures, either concurrently or separately. The dimensions and
topological nature of the metallic channels are determined by following the
spatial distribution of the charge density and the spin-texture. The results
validate the proof of concept for obtaining spontaneously forming
two-dimensional TI-conducting channels embedded into three-dimensional
insulating environments without any vacuum interfaces. Since spinodal
decomposition is a controllable kinetic phenomenon, its leverage could become
the long-sought enabler for effective TI technological deployment.
