Electronic Bloch oscillation in bilayer graphene gradient superlattices
  We investigate the electronic Bloch oscillation in bilayer graphene gradient superlattices using transfer matrix method. By introducing two kinds of gradient potentials of square barriers along electrons propagation direction, we find that Bloch oscillations up to terahertz can occur. Wannier-Stark ladders, as the counterpart of Bloch oscillation, are obtained as a series of equidistant transmission peaks, and the localization of the electronic wave function is also signature of Bloch oscillation. Forthermore, the period of Bloch oscillation decreases linearly with increasing gradient of barrier potentials. 
Hemeng Cheng, Changan Li, Tianxing Ma, Li-Gang Wang, Yun Song and   Hai-Qing Lin
cond-mat.mes-hall cond-mat.mtrl-sci