Ultra-thin Topological Insulator Bi2Se3 Nanoribbons Exfoliated by Atomic Force Microscopy

TL;DR

This study demonstrates the controlled mechanical exfoliation of Bi2Se3 topological insulator nanoribbons down to a single quintuple layer using an atomic force microscope, revealing significant changes in electrical properties with thickness.

Contribution

First demonstration of AFM-based exfoliation of Bi2Se3 nanoribbons to ultra-thin layers, enabling detailed study of surface and edge state transitions in topological insulators.

Findings

Significant difference in sheet resistance between 1-2 QLs and 4-5 QLs.

Non-metallic temperature dependence in ultra-thin Bi2Se3 devices.

Potential for studying quantum spin Hall states in exfoliated nanoribbons.

Abstract

Ultra-thin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak Van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (> 50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultra-thin nanoribbons, showing drastic difference in sheet resistance between 1~2 QLs and 4~5 QLs. Transport measurement carried out on an exfoliated (\leq 5 QLs) Bi2Se3 device shows non-metallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (> 50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states.