Nicolas Leconte

University of Seoul, Korea

Open-orbit induced extreme magnetoresistance and fractional Chern insulator in graphene/h-BN
superlattices at low fields

When: 12:00-13:00 CET, June 20th (Tuesday), 2024

Where: Seminar Room, ICMM-CSIC, Campus de Cantoblanco, Madrid

In this talk, I will discuss our recent work where we report on the hitherto unexplored low magnetic field regime in ultrahigh-quality graphene/h-BN superlattices where intrinsic band structure features perturb the single-band Hofstadter butterfly picture. For magnetic fields as low as 0.1 − 1 Tesla, we uncover extreme magnetoresistance patterns, attributed to the formation of open orbits at Lifshitz transitions, providing a truly 2D experimental realization of the commonly discussed 2D theoretical open-orbit models, and illustrated through a real-space analysis of the current densities. We further observe trigonal warping-induced Landau level splitting near the secondary Dirac point in monolayer graphene superlattice, where enhanced many-body effects induce a fractional Chern insulator, a primer at such low magnetic fields. Finally, a transition from linear to parabolic Landau level dispersion is uncovered, a phenomenon we link to miniband overlap through a semiclassical analysis. Our combined theoretical-experimental study provides insights into the intricacies of the low-field fractal spectrum ahead of the quantum Hall regime.