Measured potential profile in a quantum anomalous Hall system suggests bulk-dominated current flow

TL;DR

This study reveals that in quantum anomalous Hall systems at elevated temperatures, current predominantly flows through the bulk rather than edge modes, challenging previous assumptions and highlighting dissipative electron flow.

Contribution

The paper demonstrates that measured potentials align with Laplace's equation, indicating bulk current flow at higher temperatures in quantum anomalous Hall systems, contrary to prior edge-dominant models.

Findings

Potential profiles fit Laplace's equation with uniform conductivity

Bulk current flow persists at elevated temperatures

Extrapolation suggests bulk dominance at lower temperatures

Abstract

Ideally, quantum anomalous Hall systems should display zero longitudinal resistance. Yet in experimental quantum anomalous Hall systems elevated temperature can make the longitudinal resistance finite, indicating dissipative flow of electrons. Here, we show that the measured potentials at multiple locations within a device at elevated temperature are well-described by solution of Laplace's equation, assuming spatially-uniform conductivity, suggesting non-equilibrium current flows through the two-dimensional bulk. Extrapolation suggests that at even lower temperatures current may still flow primarily through the bulk rather than, as had been assumed, through edge modes. An argument for bulk current flow previously applied to quantum Hall systems supports this picture.