Continuous-Time Random Walk with power-law waiting times — from normal diffusion to deep subdiffusion via the exponent α.
In CTRW, the walker waits for a random time τ ~ τ^(-1-α) before each step. For α<1, the mean waiting time diverges → MSD ~ t^α (subdiffusion). At α=1: normal diffusion ⟨x²⟩~t. At α<1: particles are "trapped", leading to aging, non-ergodicity, and weak ergodicity breaking (Bouchaud 1992).