Abstract: Dissipationless topologically protected states are of major interest as well as of practical importance in metrology and quantum information technology. Although topological protection can be robust theoretically, in realistic devices it is often fragile against various dissipative mechanisms, which are difficult to probe directly because of their microscopic origins. By utilizing scanning nanothermometry , we visualized and investigated microscopic mechanisms undermining the topological protection in the quantum Hall state in graphene. Our simultaneous nanoscale thermal and scanning gate microscopy enables to identify two distinct and spatially separated scattering processes. I will show how these observations reveal that the dissipation is governed by a crosstalk between counter-propagating pairs of channels that appear at graphene boundaries because of edge reconstruction due to charge accumulation at the edges.
Time permitting, I will present a semi-classical transport model quantifying the effect of edge accumulation under moderate magnetic fields and in particular the strikingly high non-local voltages it generates. I will discuss its implication for Hall measurements in particular in the case of charge-neutral graphene.
 D. Halbertal,et al., Nature 539, 407-410(2016)
 A. Marguerite, et al., Nature 575, 628-633 (2019)
 A. Aharon-Steinberg, et al., Nature 593, 528-534 (2021)
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