Kadowaki-Woods relation and thermal transport in the two-dimensional van der Waals ferromagnet Fe3GeTe2

We have studied electric and thermal transport properties in two-dimensional van der Waals ferromagnetic ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$. The low-temperature longitudinal resistivity measured in the $ab$ plane is contributed by the impurity scattering, the quantum correction, and the electron-electron interaction. Meanwhile, the low-temperature specific heat consists of linear and cubic temperature terms, corresponding to contributions of electrons and phonons, respectively. Therefore, the heavy-fermion state in ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ can be described by Landau's Fermi liquid theory. The Kadowaki-Woods ratio in ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ is five times larger and smaller than the values of transition metals and heavy-fermion compounds, respectively. Moreover, the thermal conductivity measured along the $c$ axis increases monotonically with temperature, exhibiting a phonon glass electron crystal behavior, due to the dominant role of boundary scattering of phonons. The ${T}^{1.35}$ dependence of the lattice thermal conductivity observed at low temperatures arises from a combined effect of the highly anisotropic dispersion and strong impurity scattering of phonons.