Bias controlled switching of spin polarization between ν = ±1 quantum Hall edges at graphene pn junction

Differentiating between the ground states of the half-filled zeroth Landau level in graphene is the key to

understand their low-energy excitations. One promising route for this is to study the effects of different

ground states of ν = 0 filling on nearby edge states belonging to fillings |ν| > 0. In this regard, graphene

pn junction is an ideal platform, as in the symmetry broken quantum Hall (QH) regime, the co-propagating

electron and hole-like edge states at the junction are separated by a narrow ν = 0 region. Here, we report

bias controlled tunneling between ν = ±1 QH edges in a graphite gated hBN encapsulated monolayer

graphene device. At zero bias, we observe finite tunneling (t ∼ 0.5), which remains almost constant up

to ∼ 120μV at 8T. Strikingly, above ∼ 120μV the tunnelling sharply falls and exhibits repeated smaller

peaks at discrete energies before vanishing completely. Moreover, the tunneling shows unique dependence

on filling, magnetic field and temperature. The tunneling at zero bias is anomalous as it is is expected to

be zero between ν = ±1 edges due to their orthogonal spin polarization. Thus, from tunneling to fully

blockade suggests bias-controlled switching of spin polarization between ν = ±1 edges, which is further

corroborated with our detailed theoretical calculations.