Granular topological insulators

TL;DR

This study investigates how granularity influences the properties of topological insulators, revealing that granular Bi2Se3 thin films retain topological surface states with unique characteristics, enabling new engineering possibilities.

Contribution

It demonstrates that granularity can preserve and modify topological surface states, providing a new platform for designing topological insulators with tunable properties.

Findings

Topological surface states are observed in granular Bi2Se3 films.

Distinct surface state coupling-decoupling transitions are identified.

Large surface state penetration depths and exotic Berry phase effects are reported.

Abstract

Granular conductors form an artificially engineered class of solid state materials wherein the microstructure can be tuned to mimic a wide range of otherwise inaccessible physical systems. At the same time, topological insulators (TIs) have become a cornerstone of modern condensed matter physics as materials hosting metallic states on the surface and insulating in the bulk. However it remains to be understood how granularity affects this new and exotic phase of matter. We perform electrical transport experiments on highly granular topological insulator thin films of Bi$_2$Se$_3$ and reveal remarkable properties. We observe clear signatures of topological surface states despite granularity with distinctly different properties from conventional bulk TI systems including sharp surface state coupling-decoupling transitions, large surface state penetration depths and exotic Berry phase effects. We present a model which explains these results. Our findings illustrate that granularity can be used to engineer designer TIs, at the same time allowing easy access to the Dirac-fermion physics that is inaccessible in single crystal systems.