Thermal Transport Study of Broken Symmetry Quantum Hall States Using Noise Thermometry

A number of phases with spontaneously broken symmetry, including canted-antiferromagnetism and valley-polarized states, are predicted to be present in the half-filled zero-energy Landau level of graphene. While results from charge-based transport measurements concur with the theory, a more direct probe is needed to demonstrate that neutral modes, such as spin and valley waves, exist in the insulating phases. Using a non-local noise measurement technique, where graphene serves as nanoscale heater and thermometer, we extract the thermal conductance of graphene at $\nu=0$ and observe thermal transport signatures of a phase transition between two different broken symmetry states, consistent with theory. Thermal transport measurement offers a new route towards understanding the intriguing spontaneous symmetry breaking in quantum Hall regimes in graphene and other van der Waals materials.