Abstract: A nanoscale SQUID fabricated on the apex of a quartz pipette (a ‘SQUID-on-tip’) can be used as an ultra-sensitive scanning probe to measure local magnetic fields. Utilizing such a scanning SQUID-on-tip, I will describe an experiment to image equilibrium currents in the quantum Hall regime in magic angle graphene to obtain tomographic imaging of Landau levels and map their local evolution with carrier density. This renders a nanoscale high precision map of the local twist-angle and reveals substantial twist-angle gradients and a network of jumps [1]. We show that the twist-angle gradients generate large gate-tunable in-plane electric fields, unscreened even in the metallic regions, which drastically alter the quantum Hall state by forming edge channels in the bulk of the samples. The correlated states are found to be particularly fragile with respect to twist-angle disorder. We establish the twist-angle disorder as a fundamentally new kind of disorder, which alters the local band structure and may significantly affect the correlated and superconducting states. [1] A. Uri, S. Grover, Y. Cao, J. A. Crosse, K. Bagani, D. Rodan-Legrain, Y. Myasoedov, K. Watanabe, T. Taniguchi, P. Moon, M. Koshino, P. Jarillo-Herrero, and E. Zeldov, Nature 581, 47 (2020) Meeting ID: 969 5855 0632
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