Absence of heat flow in ν = 0 quantum Hall ferromagnet in bilayer graphene

The charge neutrality point of bilayer graphene, denoted as the ν = 0 state, manifests competing phases marked by spontaneous ordering of the spin, valley and layer degrees of freedom under external magnetic and electric fields. However, due to their electrically insulating nature, identifying these phases through electrical conductance measurements is a challenge. A recent theoretical proposal suggests that thermal transport measurements can detect these competing phases. Here we experimentally show that the bulk thermal transport of the ν = 0 state in bilayer graphene vanishes. This is in contrast to the theory, which predicts a finite thermal conductance in the ν = 0 state. By varying the external electric field and conducting temperature-dependent measurements, our results suggest that there are gapped collective excitations in the ν = 0 state. Our findings underscore the necessity for further investigations into the nature of the ν = 0 state.