The « Physique Mésoscopique » team from the Physics Laboratory of the Ecole Normale Supérieure recently published an article in Nature physics.
The authors :
- Raphaëlle DELAGRANGE
- Manjari GARG
- Gaëlle LE BRETON
- Aifei ZHANG
- Quan DONG
- Yong JIN
- Kenji WATANABE
- Takashi TANIGUCHI
- Preden ROULLEAU
- Olivier MAILLET
- Patrice ROCHE
- François PARMENTIER
Under high perpendicular magnetic field and at low temperatures, graphene develops an insulating state at the charge neutrality point. This state, dubbed nu=0, is due to the interplay between electronic interactions and the four-fold spin and valley degeneracies in the flat band formed by the n=0 Landau level. Determining the ground state of nu=0, including its spin and valley polarization, has been a theoretical and experimental undertaking for almost two decades. Here, we present experiments probing the bulk thermal transport properties of monolayer graphene at nu=0, which directly probe its ground state and collective excitations. We observe a vanishing bulk thermal transport, in contradiction with the expected ground state, predicted to have a finite thermal conductance even at very low temperature. Our result highlight the need for further investigations on the nature of nu=0.
© François Parmentier – CNRS
The four possible ground states of ν=0, shown as two spins (red and blue arrows) distributed on the honeycomb lattice of graphene.
Yellow: antiferromagnetic phase: the two opposite pins reside on a separate sublattice.
Purple: ferromagnetic phase: the two spins are aligned, each on its sublattice.
Orange: Kekule distortion phase: the two opposite spins live on a superposition of the two sublattices.
Cyan: sublattice polarized phase: the two opposite spins live on the same sublattice.
The central cartoon depicts the principle of the experiment, where heat is carried for a hot electrode (red) to a cold one (purple) across ν=0. Only the antiferromagnetic and Kekule distortion phase are thermal conductors at low temperature.