Ineffectiveness of the triplet diffusion correction in the electron transport of disordered systems

The mystery of the field-independent ${T}^{1/2}$ behavior of resistivity in single-crystal ${\mathrm{Th}}_{2}{\mathrm{CoSi}}_{3}$ is unraveled through the lens of interacting electrons in disordered systems. Consistent with theoretical predictions, our magnetotransport studies illuminate a scenario where a robust spin-orbit interaction renders the triplet term in the diffusion contribution ineffective. As a consequence, the magnetic field exerts no influence on the diffusion correction, giving sole dominance to weak localization and classical effects in shaping the magnetoresistance. In addition, marginal temperature variation of the weak localization at low temperatures results in the ${T}^{1/2}$ relation being predominantly dictated by the singlet term in the diffusion correction.