Spin-Polarized to Valley-Polarized Transition in Graphene Bilayers at $\nu=0$ in High Magnetic Fields

TL;DR

This study reveals a transition in the quantum Hall state of graphene bilayers from spin polarization to valley polarization driven by an electric field, with the transition point linearly dependent on magnetic field strength.

Contribution

It demonstrates the electric field-induced transition between spin and valley polarized states in graphene bilayers at $ u=0$, providing new insights into their quantum Hall phase behavior.

Findings

Transition from spin to valley polarization as E increases

Linear dependence of transition E-field on magnetic B

Insulating behavior strongest near E=0 and at large E

Abstract

We investigate the transverse electric field ($E$) dependence of the $\nu$=0 quantum Hall state (QHS) in dual-gated graphene bilayers in high magnetic fields. The longitudinal resistivity ($\rho_{xx}$) measured at $\nu$=0 shows an insulating behavior which is strongest in the vicinity of $E$=0, and at large $E$-fields. At a fixed perpendicular magnetic field ($B$), the $\nu$=0 QHS undergoes a transition as a function of $E$, marked by a minimum, temperature-independent $\rho_{xx}$. This observation is explained by a transition from a spin polarized $\nu$=0 QHS at small $E$-fields, to a valley (layer) polarized $\nu$=0 QHS at large $E$-fields. The $E$-field value at which the transition occurs has a linear dependence on $B$