Distinct Quantum States in Topological Insulator Surfaces of Nanowires and Nanoribbons of Bismuth Selenide (Bi2Se3)

Topological insulators (TIs) exhibit unconventional quantum phases that can be tuned by external quantum confinements. The geometry of the surface of 3D TIs plays a crucial role. For example, the geometrical crossover from 2D surfaces to a 1D cylinder results in a novel state with a Spin-Berry Phase (SBP). Surface-Enhanced Raman Scattering (SERS) with a sub-micron spatial resolution is utilized to study the quantum-confinement effects of quasi-relativistic electrons along the perimeter of the circular bismuth selenide (Bi2Se3) nanowires. The presence of diameter-dependent SERS in nanowires can be attributed to the self-interference effect of the electronic wave-function along the circumferential direction of the TI nanowires. Nanoribbons with rectangular cross-section do not show this effect. Further gold nanoparticles are applied as plasmonic SERS sensors attached to the distinct topological surface states to manipulate quasi-relativistic surface states of nanoribbons and nanowires. This technique enables to discriminate between different geometries of TI surface states and also opens a novel pathway to probe the quantum properties of topological surface states.