1206.5881 (Wei Yan et al.)

Strain-induced Enhanced Interlayer Coupling, Landau Quantizations, and
Valley Polarization in Twisted Graphene Bilayer    [PDF]

Wei Yan, Mengxi Liu, Lan Meng, Zhao-Dong Chu, Rui-Fen Dou, Yanfeng Zhang, Zhongfan Liu, Jia-Cai Nie, Lin He

The local electronic properties of strained graphene bilayer with a twist angle \theta ~ 2.9^{\circ} were studied by scanning tunneling microscopy and spectroscopy. Our experimental result reveals: (a) the interlayer coupling strength of the twisted graphene bilayer is much enhanced around a strained graphene wrinkle; (b) the strain induces apparent Landau level quantization, which mimics the quantization of massive Dirac Fermions of graphene bilayer in a perpendicular magnetic field of about 100 T, along the graphene wrinkle; (c) the strain results in valley polarization with a gap ~ 0.30 eV along the wrinkle, i.e., the eight-fold degenerate Landau level at the charge neutrality point of graphene bilayer is splitted into two four-fold degenerate quartets polarized on each layer. The observed significant energy gap and large pseudomagnetic field suggest that the strained graphene bilayer is an ideal platform to realize high-temperature zero-field quantum valley Hall effect.

View original: http://arxiv.org/abs/1206.5881