Selective Contact and Patterning of Topological Surface States by Interfacing with Trivial and Ferromagnetic Insulators*

Topological insulators (TIs) are a novel class of material which host helical surface states with exciting and unique electronic properties. They can provide insights into new physics and also pave the way for potential spintronic applications. Much work has been done to identify and characterise these surface states, but in order to utilise them towards multifunctional devices, we need a way to control the exchange gap opening in a tailored way and pattern them accordingly. We present results from devices which allow selective contact and patterning of topological surface states. We interface a TI with a ferromagnetic insulator to open up a gap in the Dirac cone, in an effort to have independent contact to the top and bottom surface states of a single TI film, enabling the characterisation and utilisation of the two surface states separately We also study heterostructures with two TI layers separated by a trivially insulating tunnel barrier, allowing for a way of probing the dispersion relation of TIs using spin and momentum resolved tunnelling.