  We have measured the low-field magnetoresistances (MRs) of a series of
Sn-doped indium oxide thick films in the temperature $T$ range 4--35 K. The
electron dephasing rate $1/\tau_{\varphi}$ as a function of $T$ for each film
was extracted by comparing the MR data with the three-dimensional (3D)
weak-localization theoretical predictions. We found that the extracted
$1/\tau_{\varphi}$ varies linearly with $T^{3/2}$. Furthermore, at a given $T$,
$1/\tau_{\varphi}$ varies linearly with $k_F^{-5/2}l^{-3/2}$, where $k_{F}$ is
the Fermi wavenumber, and $l$ is the electron elastic mean free path. These
features are well explained in terms of the small-energy-transfer
electron-electron scattering time in 3D disordered conductors. This electron
dephasing mechanism dominates over the electron-phonon ($e$-ph) scattering
process because the carrier concentrations in our films are $\sim$ 3 orders of
magnitude lower than those in typical metals, which resulted in a greatly
suppressed $e$-ph relaxation rate.

Mesoscale and Nanoscale Physics;Disordered Systems and Neural Networks