Divergence of the effective mass in a strongly-interacting 2D electron system*

The diffusion thermopower in a low-disorder, strongly-interacting 2D electron system in silicon increases with decreasing electron density and tends to infinity at a finite density $n_t$. Comparison with earlier data for a high-disorder silicon system indicates that the critical density $n_t$ does not depend on the degree of disorder. The increase of the thermopower is associated with a diverging electron mass in the close vicinity of an interaction-induced phase transition.