Localization physics in graphene Moire superlattices

TL;DR

This study investigates how the Berry phase transition from pi to 2pi in graphene moire superlattices affects localization phenomena, revealing a transition from weak anti-localization to weak localization through magneto-conductance measurements.

Contribution

It provides the first experimental observation of Berry phase-induced localization transition in graphene superlattices, supported by quantum oscillation data and theoretical calculations.

Findings

Transition from WAL to WL observed in a single device

Berry phase shifts from pi to 2pi between PDC and CDC

Theoretical models confirm Berry phase transition effects

Abstract

Non-trivial Berry phase of graphene leads to unusual quantum correction to the conductivity. Berry phase of pi in single layer graphene (SLG) and 2pi in bi-layer graphene (BLG) is expected to reveal weak anti-localization (WAL) and weak localization (WL), respectively. However, experimentally both WAL and WL have been observed in graphene devices depending on the strength of different scattering mechanisms. Graphene superlattice having multiple Dirac cones is expected to exhibit pi to 2pi Berry phase transition from primary Dirac cone (PDC) to cloned Dirac cone (CDC). However, its effect on localization physics has not been explored yet. In this letter we present the magneto-conductance study in a hexagonal Boron-nitride (hBN)-graphene moire superlattice. Our results reveal a transition from WAL at PDC to WL at CDC in a single device by tuning the Fermi energy. The transition is supported by the quantum oscillation measurements showing a shift of pi phase from PDC to CDC and corresponding theoretical calculation capturing the Berry phase transition. Thus, our studies on localization physics in graphene superlattice pave the way to understand the carrier dynamics at multiple Dirac cones.