Weak localisation magnetoresistance and valley symmetry in graphene

TL;DR

This paper investigates how valley symmetry and scattering mechanisms in graphene influence its weak localization and magnetoresistance, revealing the interplay between symmetry-breaking effects and electron interference phenomena.

Contribution

It provides a detailed analysis of how trigonal warping and inter-valley scattering affect weak localization and magnetoresistance in graphene.

Findings

Trigonal warping suppresses weak antilocalisation.

Inter-valley scattering restores negative magnetoresistance.

Magnetoresistance depends on relaxation rates of valley symmetry breaking.

Abstract

Due to the chiral nature of electrons in a monolayer of graphite (graphene) one can expect weak antilocalisation and a positive weak-field magnetoresistance in it. However, trigonal warping (which breaks p/-p symmetry of the Fermi line in each valley) suppresses antilocalisation, while inter-valley scattering due to atomically sharp scatterers in a realistic graphene sheet or by edges in a narrow wire tends to restore conventional negative magnetoresistance. We show this by evaluating the dependence of the magnetoresistance of graphene on relaxation rates associated with various possible ways of breaking a 'hidden' valley symmetry of the system.