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.

双层石墨烯的电荷中性点表示为 ν = 0 状态，表现出在外部磁场和电场下自发排列的自旋、谷和层自由度的竞争相。然而，由于它们的电绝缘性质，通过电导测量来识别这些相是一项挑战。最近的一项理论提议表明，热传输测量可以检测到这些竞争相。在这里，我们通过实验表明，双层石墨烯中 ν = 0 态的体热传输消失了。这与预测 ν = 0 状态下有限热导的理论形成鲜明对比。通过改变外部电场和进行与温度相关的测量，我们的结果表明，在 ν = 0 状态下存在间隙集体激励。我们的研究结果强调了进一步研究 ν = 0 状态性质的必要性。