Electronic Thermal Conductance Suppression in Lightly Doped Bilayer Graphene Measured via Johnson Noise Thermometry*

Systems with strongly interacting and correlated electrons can exhibit exotic new physics, such as the hydrodynamics regime, where particles’ behavior is best collectively described as a viscous fluid rather than as individual particles. Several such systems have recently been both predicted and shown experimentally to have thermal conductivity enhanced or reduced relative to the near-universal Lorentz value expected from Wiedemann-Franz Law. Bilayer graphene presents a strong candidacy for quantum criticality and hydrodynamics at charge neutrality, where the carrier-carrier Coulomb energy dominates the kinetic energy of quasiparticles. We explore such behavior by measuring the electronic thermal conductivity of bilayer graphene encapsulated in boron nitride and gated by dual graphite gates, with residual density below 3×10¹⁰ cm^-2. We use our high-frequency Johnson noise thermometry technique to measure the electronic cooling of the electron system, extracting out the thermal conductivity. We observe a large reduction of the thermal conductivity below the Wiedemann Franz Law at electron doping slightly away from charge neutrality. We discuss these results in the context of hydrodynamics.