Topological protection revealed by real-time longitudinal and transverse studies

Abstract

Topology provides an essential concept for achieving unchanged (or protected) quantum properties in the presence of perturbations. A challenge facing realistic applications is that the level of protection displayed in real systems is subject to substantial variations. Some key differences stem from mechanisms influencing the reconstruction behaviors of extended dissipationless modes. Despite various insightful results on potential causes of backscattering, the edge-state-based approach is limited because the bulk states, as shown by breakdown tests, contribute indispensably. This study investigates the influence of bulk reconstruction where dissipationless modes are global objects instead of being restricted to the sample edge. An integer quantum Hall effect (IQHE) hosted in a Corbino sample geometry is adopted and brought continuously to the verge of a breakdown. A detection technique is developed to include two independent setups capable of simultaneously capturing the onset of dissipation in both longitudinal and transverse directions. The real-time correspondence between orthogonal results confirms two facts. 1. Dissipationless charge modes undergo frequent reconstruction in response to electrochemical potential changes, causing dissipationless current paths to expand transversely into the bulk while preserving chirality. A breakdown only occurs when a backscattering emerges between reconfigured dissipationless current paths bridging opposite edge contacts. 2. Impurity screening is vital in enhancing protection, and topological protection is subject to an intriguing interplay of disorder, electron-electron interaction, and topology. The proposed reconstruction mechanism qualitatively explains the robustness variations, beneficial for developing means for optimization.