Unveiling the Landau Levels Structure of Graphene Nanoribbons

Magnetotransport measurements are performed in ultraclean (lithographically patterned) graphene nanoribbons down to 70 nm. At high magnetic fields, a fragmentation of the electronic spectrum into a Landau levels pattern with unusual features is unveiled. The singular Landau spectrum reveals large magneto-oscillations of the Fermi energy and valley degeneracy lifting. Quantum simulations suggest some disorder threshold at the origin of mixing between opposite chiral magnetic edge states and disappearance of quantum Hall effect.