Shubnikov-de Haas oscillations in p and n-type topological insulator (Bi$_{x}$Sb$_{1-x}$)$_{2}$Te$_{3}$

TL;DR

This study observes Shubnikov-de Haas oscillations in topological insulator films with tunable carrier types, revealing how Fermi-level adjustments influence Berry phase, mobility, and surface versus bulk conduction dominance.

Contribution

It demonstrates control over topological insulator transport properties by tuning composition, highlighting the transition from bulk metallic to surface-dominated conduction.

Findings

High mobility of 17,000 cm^2/V/s in n-type sample

Observation of π Berry phase in n-type sample

Transition from 2π to π Berry phase with composition tuning

Abstract

We show Shubnikov-de Haas oscillations in topological insulator (Bi$_{x}$Sb$_{1-x}$)$_{2}$Te$_{3}$ films whose carrier type is p-type (x = 0.29, 0.34) and n-type (x = 0.42). The physical properties such as the Berry phase, mobility, and the scattering time are significantly changed by tuning the Fermi-level position with the concentration x. The Landau-level fan diagram in the sample with x = 0.42 showed the $\pi$ Berry phase and its mobility was as high as 17,000 cm$^{2}$/V/s, whereas the others had the 2$\pi$ Berry phase and much lower mobility. This suggests that because the bulk band of the sample with x = 0.42 does not cross the Fermi level, it becomes bulk insulating, resulting in the topological surface-state dominating transport. Thus, we can switch sample properties from degenerate to bulk insulating by tuning the concentration x, which is consistent with results of angle-resolved photoemission spectroscopy.