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

The charge neutrality point of bilayer graphene exhibits interaction induced spontaneously isospin (spin/valley/layer) symmetries broken phases under external magnetic and electric fields. However, the electrically insulating nature of these phases makes their identification quite challangeing in conventional electrical conductance measurements. Inspired by a recent theoretical proposal based on the thermal transport approach, we experimentally explore the bulk thermal transport of the ν = 0 state in bilayer graphene to investigate its ground states and collective excitations associated with isospin. While the theory anticipates a finite thermal conductance in the ν = 0 state, our findings unveil an absence of detectable thermal conductance. Through variations in the external electric field and temperature-dependent measurements, our results suggest gapped collective excitations at ν = 0 state. Our findings underscore the necessity for further investigations into the nature of ν = 0.