Emergent Negative Differential Resistance with an Undisturbed Topological Surface State

Emergent properties in topological insulator heter-ostructures offer fresh insight not only to understand the system as a whole but also to design new approaches to device engineering at the nanoscale. Here we report the emergent phenomenon of negative differential resistance (NDR) on a topological insulator substrate. Starting with the spin-bearing cobalt fluorophthalocya-nine molecule F16CoPc as the fundamental building block and the topological insulator (TI) Bi2Se3 as the host, using scanning tunneling spectroscopy (STS) we observe the emergence of NDR at the F16CoPc/Bi2Se3 interface at a specific negative bias. The topological surface state is also preserved in the process. Realizing NDR at the molecular scale presents a major advance toward designing ultrafast electron tunneling devices as well as high speed, low power, and compact nanoelectronic devices. The undisturbed topological surface state of Bi2Se3 offers added tunability for computer architectures that can be built concomitantly using the topological surface state and NDR.