Valley Current in Graphene Through Electron-Phonon Interaction

Abstract

Valleytronics which has a lot of advances in the information processing and communication requires the manipulation of the valley degree of freedom of the carriers. In this thesis, we discuss valley current, which is carried by quasiparticles in graphene. We show that the valley current arises owing to a peculiar term in the electron-phonon collision integral that mixes the scalar and vector gauge-field-like vertices in the electron-phonon interaction. This mixing makes collisions of phonons with electrons sensitive to their chirality, which is opposite in two valleys. As a result of collisions with phonons, electrons of the different valleys deviate in opposite directions. The valley-dependent deviation of the quasiparticle current does not request for breaking the spatial inversion symmetry. The effect exists both in pristine graphene or bilayer graphene samples, and it increases with temperature owing to a higher rate of collisions with phonons at higher temperatures. The valley current carried by quasiparticles could be detected by measuring the electric current using a nonlocal transformer of a suitable design. This could open up another unexplored possibility in the area of valleytronics.