Transition from weak antilocalization (WAL) to strong localization in ultrathin TI thin films. (a) In the diffusive transport regime, the zero-field conductivity σ has a logarithmic dependence on temperature, and the magnetoconductivity shows the WAL behavior described by Eq. (1). (b) In the intermediate transport regime between the WAL and the strong localization, the magnetoconductivity is still negative but the magnitude is reduced significantly. (c) In the strong localization regime, the low field magnetoconductivities are positive and the zero-field sheet resistivity follows ρ_xx ∝ exp(T^1/3), suggesting the transport in the variable range hopping regime. Adapted from Ref. [40].