T-square resistivity without Umklapp scattering in dilute metallic Bi₂O₂Se

Fermi liquids (FLs) display a quadratic temperature (T) dependent resistivity. This can be caused by electron-electron (e-e) scattering in presence of inter-band or Umklapp scattering. However, dilute metallic SrTiO₃ was found to display T² resistivity in absence of either of the two mechanisms. The presence of soft phonons as possible scattering centers raised the suspicion that T² resistivity is not due to e-e scattering. Here, we present the case of Bi₂O₂Se, a layered semiconductor with hard phonons, which becomes a dilute metal with a small single-component Fermi surface upon doping. It displays T² resistivity well below the degeneracy temperature in absence of Umklapp and inter-band scattering. We observe a universal scaling between the T² resistivity prefactor (A) and the Fermi energy (E_F), an extension of the Kadowaki-Woods plot to dilute metals. Our results imply the absence of a satisfactory understanding of the ubiquity of e-e T² resistivity in FLs.