Electronic thermal resistivity and quasiparticle collision cross section in semimetals

Electron-electron collisions lead to a T-square component in the electrical resistivity of Fermi liquids. The case of liquid 3He illustrates that the thermal resistivity of a Fermi liquid has a T-square term, expressed in m x W-1. Its natural units are h<overline>/kFEF2. Here, we present a high-resolution study of the thermal conductivity in bismuth, employing magnetic field to extract the tiny electronic component of the total thermal conductivity and resolving signals as small as approximate to 60 mu K. We find that the electronic thermal resistivity follows a T-square temperature dependence with a prefactor twice larger than the electric T-square prefactor. Adding this information to what has been known for other semimetals, we find that the prefactor of the T-square thermal resistivity scales with the square of the inverse of the Fermi temperature, implying that the dimensionless fermion-fermion collision cross section is roughly proportional to the Fermi wavelength, indicating that it is not simply set by the strength of the Coulomb interaction.