DIFFUSION ANOMALY NEAR STRUCTURAL PHASE-TRANSITIONS

We consider the diffusion of a particle coupled to a surface which undergoes a structural phase transition. Using a recently developed microscopic theory of diffusion we show that the diffusion coefficient is anomalously reduced near the transition because of diverging value of the friction near the transition. To demonstrate this anomaly, we evaluate the diffusion coefficient for a model Hamiltonian describing an adatom on the W(100) surface which undergoes a (1 x 1) --> c(2 x 2) reconstruction.