Negative and Positive Magnetoresistance in Bilayer Graphene: Effects of Weak Localization and Charge Inhomogeneity

TL;DR

This study investigates magnetoresistance in bilayer graphene, revealing the roles of weak localization, charge inhomogeneity, and electron-electron interactions across various gate voltages and temperatures.

Contribution

It provides detailed analysis of multiple magnetoresistance contributions in bilayer graphene, highlighting the dominant role of electron-electron Nyquist scattering in phase decoherence.

Findings

Weak localization observed at all gate voltages and temperatures.

Phase coherence length does not saturate at low temperatures.

Inhomogeneous charge transport causes weak positive magnetoresistance at higher fields.

Abstract

We report measurements of magnetoresistance in bilayer graphene as a function of gate voltage (carrier density) and temperature. We examine multiple contributions to the magnetoresistance, including those of weak localization (WL), universal conductance fluctuations (UCF), and inhomogeneous charge transport. A clear WL signal is evident at all measured gate voltages (in the hole doped regime) and temperature ranges (from 0.25 K to 4.3 K), and the phase coherence length extracted from WL data does not saturate at low temperatures. The WL data is fit to demonstrate that electron-electron Nyquist scattering is the major source of phase decoherence. A decrease in UCF amplitude with increasing gate voltage and temperature is shown to be consistent with a corresponding decrease in the phase coherence length. In addition, a weak positive magnetoresistance at higher magnetic fields is observed, and attributed to inhomogeneous charge transport.