Measured Potential Profile in a Quantum Anomalous Hall System Suggests Bulk-Dominated Current Flow

Area of Science:

• Condensed matter physics
• Quantum phenomena
• Topological materials

Background:

• Quantum anomalous Hall (QAH) systems ideally exhibit zero longitudinal resistance.
• Experimental QAH systems often show finite longitudinal resistance at elevated temperatures, indicating electron dissipation.
• This dissipation has been attributed to bulk current flow, challenging the idealized edge-mode transport.

Purpose of the Study:

• To investigate the dominant current flow mechanism in experimental QAH systems at elevated temperatures.
• To determine if bulk current flow persists at lower temperatures, contrary to prevailing assumptions.
• To provide a theoretical framework for understanding dissipation in QAH systems.

Main Methods:

• Measurement of potentials at multiple locations within a QAH device at elevated temperatures.
• Modeling of potential distribution using Laplace's equation with spatially uniform conductivity.
• Extrapolation of results to predict current flow at lower temperatures.

Main Results:

• Measured potentials are well described by Laplace's equation, assuming uniform bulk conductivity.
• This suggests that non-equilibrium current flows through the 2D bulk of the material.
• Extrapolation indicates that bulk current flow may be dominant even at lower temperatures.

Conclusions:

• Current flow in experimental QAH systems may primarily occur through the bulk, not exclusively edge modes, even at low temperatures.
• This challenges the conventional understanding of transport in QAH systems.
• The findings support a model of bulk current flow, consistent with theories applied to quantum Hall systems.