Observation of a topologically non-trivial surface state in half-Heusler PtLuSb (001) thin films

Topological insulators are a recently discovered new quantum state of matter that has a bulk band gap but also possesses cross-gap surface states which are protected by time-reversal symmetry. The experimental realization of topologically non-trivial surface states (TSSs) in materials such as Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ has generated widespread interest in identifying other material systems that exhibit TSSs due to their many uses including spintronic devices. In particular, recent theory calculations suggest that TSSs may be found in certain half-Heusler ternary compounds. If experimentally realizable, this would provide an opportunity for the creation of entirely new heterostructure spintronic devices that make use of the structurally-identical but electronically-varied nature of Heusler compounds. Here, we show the presence of a TSS in the half-Heusler compound PtLuSb. Spin and angle-resolved photoemission spectroscopy reveals a surface state with linear dispersion and a helical tangential spin texture consistent with theoretical predictions and the expectation for a topological insulator.