Strong spin-dephasing in a topological insulator-paramagnet heterostructure

The interface between magnetic materials and topological insulators can drive the formation of exotic phases of matter and enable functionality through the manipulation of the strong spin polarized transport. Here, we report that the transport processes that rely on strong spin-momentum locking in the topological insulator Bi2Se3 are completely suppressed by scattering at a heterointerface with the kagome-lattice paramagnet, Co7Se8. Bi2Se3–Co7Se8–Bi2Se3 trilayer heterostructures were grown using molecular beam epitaxy, where magnetotransport measurements revealed a substantial suppression of the weak antilocalization effect for Co7Se8 at thicknesses as thin as a monolayer, indicating a strong dephasing mechanism. Bi2−xCoxSe3 films, in which Co is in a non-magnetic 3+ state, show weak antilocalization that survives to higher than x = 0.4, which, in comparison with the heterostructures, suggests that the unordered moments of Co2+ act as a far stronger dephasing element. This work highlights several important points regarding coherent transport processes involving spin-momentum locking in topological insulator interfaces and how magnetic materials can be integrated with topological materials to realize both exotic phases and novel device functionality.