Excess resistivity in graphene superlattices caused by umklapp electron-electron scattering
Journal: Nature Physics
Publication Date: 15 October, 2018
Umklapp electron-electron scattering in graphene heterostructures
Umklapp electron-electron scattering (Uee) is the process that gives pure metals an electrical resistance. In this process, two electrons scatter from each other, simultaneously, transferring to the solid a momentum determined by the reciprocal lattice vector of the crystal. It is, however, difficult to measure umklapp scattering in clean metals, because it is often masked by other dissipation phenomena. Researchers at National Graphene Institute have shown that umklapp electron-electron scattering dominates the transport properties of superlattices made by placing layers of graphene on top of hexagonal boron nitride (hBN). Aligning graphene with an hBN substrate produces a moiré pattern with a period of around 15 nm when the two materials are perfectly aligned, generating a periodic superlattice potential that alters the materials electronic properties. Uee processes in these heterostructures are one of the dramatic moire superlattice effects, and they lead to a giant excess resistivity when the superlattice has a long period, causing the room-temperature mobility of devices to plummet, when compared to non-superlattice graphene devices. This effect would limit the potential applications of graphene in high-mobility devices operating a room temperature, unless the problem is overcome by misaligning (twisting) graphene and hBN with respect to each other.
- Graphene in highly aligned heterostructures with hexagonal boron nitride acquires high room-temperature resistivity