Thermal transfer enhancement by hydrodynamic plasmons in electron bilayers*

We develop a theory of heat transfer induced by thermal charge fluctuations in two-dimensional electron double layers. 

We consider pristine systems comprised of identical layers, and focus on the regime of sufficiently high temperatures and interlayer distances d, where the relevant charge fluctuations may be described using the hydrodynamic approach. In this limit heat transfer is dominated by the plasmon resonances. For systems with Galilean-invariant electron dispersion the interlayer thermal conductance is proportional to the kinematic viscosity of the electron liquid, and decreases as the inverse layer separation to the fourth power. In the absence of Galilean invariance thermal conductance decreases as the inverse layer separation to the third power. This strong enhancement can be traced to a drastically different broadening of plasmon resonances in systems with and without Galilean invariance.