Fig. 5: Two channels for the conduction of heat.
a Transmission by quasi-particles is dominant at low temperatures. Collisions in momentum space between quasi-particles lead to a ∝ T−2 transmission. b Transmission by collective response of the Fermi surface. The amplitude of transmission, set by the square of the Fermi radius and the de Broglie thermal wavelength, the thermal thickness of the Fermi surface, is ∝ T −1/2. c Sound mode with a 2kF wavevector has a wavelength of the order of the interatomic distance. A thermal gradient will cancel the equivalency between two modes propagating in opposite orientations.
