Exceptional topological robustness probed by real-time bulk and edge measurements

Though topology-themed studies are progressing in several aspects, what controls the topological robustness (or fragility) remains an unresolved fundamental question. Studies of the protected edge states so far attribute the variations in the robustness level primarily to the disorder effects. However, the findings cannot address the more general effect of topological breakdowns that necessarily involve the bulk states. Unlike the edge states, probing the bulk excitations is notoriously nontrivial. First, probing an enormous insulator requires an unconventional setup capable of accurately capturing dynamic responses in ultra-high impedance limits. Second, even if an appropriate bulk probe is found, detecting the bulk remains challenging because there exist reconstruction effects possessing random and dynamic features percolating over larger length scales. Here, a new method is demonstrated that enables such a real-time measurement in the integer quantum Hall effect (IQHE) hosted in a Corbino geometry. The extra pair of edge channels are utilized as parallel line probes to the bulk states. This setup allows completely independent measurement of the bulk and edge states so that appropriate sourcing/sensing techniques methods are set up to accurately detect conductors and insulators at the same time. Rendering the IQHE to the verge of a breakdown, accurately measured insulating and conducting responses reveal exceptionally more robust topological protection in a strongly correlated limit than in weakly interacting systems. The cause of the breakdown is identified as back-scatterings arising between dissipationless current paths of opposite chirality facilitated by rare local resonant tunnelings. A unique ``staircase" bulk feature, captured in real-time correspondence with the emergence of edge dissipation and deviation from Hall quantization, indicates a dielectric reconstruction effect influenced by enhanced impurity screening due to strong electron-electron interaction. These findings provide new insight into optimizing topological robustness, as well as pave the road for pursuing instrinic topology in strongly correlated limits.