Fragility of the Dirac Cone Splitting in Topological Crystalline Insulator Heterostructures

• Published in: ACS nano Vol. 12; no. 1; pp. 617 - 626
• Main Authors: Polley, Craig M, Buczko, Ryszard, Forsman, Alexander, Dziawa, Piotr, Szczerbakow, Andrzej, Rechciński, Rafał, Kowalski, Bogdan J, Story, Tomasz, Trzyna, Małgorzata, Bianchi, Marco, Grubišić Čabo, Antonija, Hofmann, Philip, Tjernberg, Oscar, Balasubramanian, Thiagarajan
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.01.2018
• Subjects: angle-resolved photoemission spectroscopy (ARPES); Condensed Matter Physics; Den kondenserade materiens fysik; Engineering and Technology; Fysik; Nano Technology; Nanoteknik; Natural Sciences; Naturvetenskap; Physical Sciences; quantum confinement; Teknik; topological crystalline insulator; topological heterostructure; valley splitting; topological heterostructure; topological crystalline insulator; valley splitting; angle-resolved photoemission spectroscopy (ARPES); quantum confinement
• ISSN: 1936-0851; 1936-086X; 1936-086X
• DOI: 10.1021/acsnano.7b07502

The “double Dirac cone” 2D topological interface states found on the (001) faces of topological crystalline insulators such as Pb1–x Sn x Se feature degeneracies located away from time reversal invariant momenta and are a manifestation of both mirror symmetry protection and valley interactions. Similar shifted degeneracies in 1D interface states have been highlighted as a potential basis for a topological transistor, but realizing such a device will require a detailed understanding of the intervalley physics involved. In addition, the operation of this or similar devices outside of ultrahigh vacuum will require encapsulation, and the consequences of this for the topological interface state must be understood. Here we address both topics for the case of 2D surface states using angle-resolved photoemission spectroscopy. We examine bulk Pb1–x Sn x Se­(001) crystals overgrown with PbSe, realizing trivial/topological heterostructures. We demonstrate that the valley interaction that splits the two Dirac cones at each X̅ is extremely sensitive to atomic-scale details of the surface, exhibiting non-monotonic changes as PbSe deposition proceeds. This includes an apparent total collapse of the splitting for sub-monolayer coverage, eliminating the Lifshitz transition. For a large overlayer thickness we observe quantized PbSe states, possibly reflecting a symmetry confinement mechanism at the buried topological interface.