Study On High Magnetic Tunneling Spectra Of AB-stacked Bilayer And ABC-stacked Trilayer Graphene

Graphene has become a star material in physics research because of its unique electrical properties,and its electronic characteristics change with the number of layers and the stacking order between layers.For example,due to multiple electron degrees of freedom,AB-stacked bilayer graphene has gradually become a very attractive experimental material for exploring the rich and novel phenomena in the quantum Hall mechanism.In addition,due to the almost non-dispersive flat band structure near the charge neutral point of the ABC-stacked graphene trilayer,it is expected to exhibit a novel many-body phenomenon.Here we used the ultralow-temperature and highmagnetic-field scanning tunneling microscopy and spectroscopy to study the Landau level spectrum of AB-stacked bilayer and ABC-stacked trilayer graphene and observed rich broken-symmetry-induced Landau level splittings,including valley,spin,and orbit splittings.The main results obtained are as follows:First of all,in the study of high magnetic field tunneling spectra of AB-stacked bilayer graphene,our experiments show that the spin and orbital splitting of the lowest orbital index n=(0,1)Landau level are dependent on its filling state,and show a significant enhancement in the partially filled state.The splitting of the fully filled valley polarization Landau level is also enhanced when the opposite valley Landau level is partially filled.These results reveal significant many-body effects in this system.In addition,when the Landau level of the orbital index n=(0,1)is halffilled(filling factor v=0),we directly observe the single-particle intermediate v=0phase,which is the transition state between canted anti-ferromagnetic and layerpolarized states in the bilayer graphene.Our atomic scale scanning tunneling spectroscopy measurements directly prove that this v=0 intermediate state is the predicted orbital polarization phase.In addition,in the study of the Landau level spectrum of ABC-stacked trilayer graphene,we found that the valley and spin splitting in the ABC-stacked trilayer graphene increased approximately linearly with the change of the magnetic field and the size of the spin splitting decreases as the Landau level index increases.When the Landau level of the lowest orbital index is partially filled,we find that spin splitting is significantly enhanced,which is attributed to the strong many-body effect.In addition,we observed that the lifetime of quasiparticles decreases with the energy increasing,which is also due to the strong electron-electron interaction in the ABC-stacked trilayer graphene.Our results imply an interesting fracture symmetry state and a new electronrelated effect in the ABC-stacked graphene trilayer in the presence of a high magnetic field.