Probing the topological properties of Bismuth, a second order topological insulator

Higher Order Topological Insulators are a new family of materials whose conduction paths are located not at the crystal boundaries but at the boundary of the boundaries: Thus, three dimensional Second Order Topological Insulators should conduct via one dimensional paths at the crystal hinges. In the talk I will demonstrate how mesoscopic physics experiments (along with some theory!) led to the discovery that Bismuth was the first example of a solid state Second Order Topological Insulators [1]. I will show how we detected such hinge states in monocrystalline nanowires connected to superconducting contacts, and further used the supercurrent-versus-phase relation [2,3] to demonstrate their ballistic nature. I will also present our recent measurement of the nanowire’s linear response to an ac phase difference excitation. I will argue that the response’s sharp dissipation peak when the superconducting phase difference is π is a telltale sign of topological protection at the hinges [4,5].

[1] Schindler et al, Nat. Phys. 14, 918 (2018).
[2] Murani et al., Nat. Comm. 8,15941 (2017).
[3] Beenakker, https://www.condmatjclub.org/uploads/2018/03/JCCM_March_2018_01.pdf
[4] L. Fu and C. L. Kane, Phys. Rev. B 79, 161408 (R) (2009).
[5] Murani et al., Phys.Rev. B 96, 165415 (2017); Murani et al., Phys. Rev. Lett. 122, 076802 (2019).