Magnetotransport study of the mini-Dirac cone in AB-stacked four- to six-layer graphene under perpendicular electric field

TL;DR

This study experimentally investigates Landau levels in AB-stacked four- to six-layer graphene under perpendicular electric fields, revealing mini-Dirac cones and their influence on the Landau level structure, with implications for multilayer graphene electronic properties.

Contribution

It provides the first experimental observation of mini-Dirac cones in multilayer graphene under electric fields and links their formation to trigonal warping effects.

Findings

Observation of six- and twelve-fold degenerate Landau levels near charge neutrality.

Electron-hole symmetry in four-layer graphene; asymmetry in five- and six-layer graphene.

Trigonal warping significantly influences Landau level structure at low magnetic fields.

Abstract

Landau levels of AB-stacked four- to six-layer graphene were studied experimentally in the presence of a perpendicular electric field. The Landau levels at a low magnetic field showed a characteristic structure that originated from the mini-Dirac cones created by the perpendicular electric fields. Six-fold or twelve-fold degenerate Landau levels arising from the mini-Dirac cones were observed in the vicinity of the charge neutrality point as a radial structure in a plot of their Landau fan diagrams. The structure of four-layer graphene had approximate electron-hole symmetry near the charge neutrality point, while the five- and six-layer graphene showed asymmetry. Numerical calculations of the dispersion relation and Landau level spectra indicated that trigonal warping played an essential role in forming the experimentally observed Landau level structure in low magnetic fields. In high magnetic fields, trigonal warping becomes less significant and the Landau level spectra become simpler, approaching those that were calculated without considering trigonal warping. The appearance of mini-Dirac cones in a perpendicular electric field would be a common feature of AB-stacked multilayer graphene.