Robust Topological Conduction in Bi2 Bi2Se3 Superlattices at Ambient Conditions

Abstract

Topologically protected surface states have garnered significant attention due to their robustness against perturbations and potential applications in optoelectronics. Bi2 Bi2Se3 is a topological semimetal composed of a 2D bismuthene sheet and a Bi2Se3 quintuple layer, forming an intrinsic superlattice. This study investigates the electronic structure and edge states of Bi2 Bi2Se3 [001] oriented films under ambient conditions through conducting atomic force microscopy (C-AFM). Point I-V spectroscopy and current imaging are used to characterize the surface and local transport properties of bismuthene and Bi2Se3 terminated layers. Our measurements reveal force dependent shifts in conduction mechanisms in both bismuthene and Bi2Se3, transitioning from direct tunneling (DT) at low forces and low biases, to Fowler Nordheim tunneling (FNT) at low forces and high biases, and eventually to a more ohmic like behavior at the highest forces. Under DT conditions on the bismuthene termination, we observed the Dirac cone in the dI/dV spectroscopy. Edge states are observed along the perimeter of the (001) terraces for both terminations, and are observed to have higher conductivity than the local terrace. Force-dependent imaging revealed an increase in the width of the edge state as force increased, until the conductive edge state appeared to cover the entire terrace. Furthermore, terrace heights display a force dependent distortion from the high tip forces, which indicates that the transition to the ohmic-like contact regime on either termination results from a complex interplay between strain and tip induced effects. All measurements were performed under ambient conditions, which demonstrates the robustness of the topological and edge states to ambient conditions.