Influence of Device Geometry on Transport Properties of Topological Insulator Microflakes

TL;DR

This study demonstrates how the geometry of topological insulator microflakes significantly influences transport measurements, affecting resistivity and Hall effect readings, with implications for accurate characterization.

Contribution

We show that sample geometry impacts transport measurements in topological insulators, necessitating correction factors for precise resistivity and Hall effect analysis.

Findings

Geometry correction factors are essential for accurate resistivity measurements.

Sample shape affects magnetic field dependence of transport properties.

Inhomogeneous current distribution can cause positive magnetoresistance and nonlinear Hall effect.

Abstract

In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. Here, based on finite element analysis, we show that for the non-Hall-bar shaped topological insulator samples, the measured four-point resistances can be substantially modified by the sample geometry, bulk and surface resistivities, and magnetic field. Geometry correction factors must be introduced for accurately converting the four-point resistances to the longitudinal resistivity and Hall resistivity. The magnetic field dependence of inhomogeneous current density distribution can lead to pronounced positive magnetoresistance and nonlinear Hall effect that would not exist in the samples of ideal Hall bar geometry.