Strong signature of Landau level fan from high order moiré pattern in double aligned graphene heterostructures

The moiré pattern in graphene heterostructures provides a great opportunity to study the energy spectrum of moving charge carriers in both a periodic potential and a magnetic field, the famous Hofstadter energy spectrum. Because of the suitable length scale of the periodic potential induced by the moiré pattern, it become possible to use laboratory accessible magnetic field to measure the Hofstadter energy spectrum. However, as the maximum periodicity of the moiré pattern in graphene heterostructures is approximately 14 nm, so far the measurable Hofstadter energy spectrum is limited to the first Bloch band. In this work, we report the transport measurement of double aligned graphene heterostructures. We observe strong signature of Landau level fan of a second order moiré pattern due to the interference of the moiré patterns from top and bottom graphene surfaces. The periodicity of the second order moiré pattern is about double the maximum periodicity of moiré patterns in graphene heterostructures. Our work indicates the second order moiré pattern in graphene heterostructures may make it possible to measure the high Bloch bands in Hofstadter energy spectrum.