Evidence for an Intermediate Phase below the Critical Density for the MI transition in silicon MOSFETs

The magnetoconductivity of the strongly interacting 2D electron system in low disorder silicon MOSFETs is found to scale with B/T throughout the insulating phase, confirming earlier measurements for densities near the metal-insulator transition n_c [1, 2]. We report further that the magnetoconductivity can be collapsed onto a single curve deep in the insulator for all densities up to approximately n* ~ 0.8 n_c. The shape of the scaled curves varies between n* and n_c, where n_c signals the entry into the metallic state. This suggests the presence of an intermediate phase between the deep insulator and the metal.

[1] S. A. Vitkalov, H. Zheng, K. M. Mertes, and M. P. Sarachik, Phys. Rev. Lett. 87, 086401 (2001).
[2] Yeekin Tsui, S. A. Vitkalov, M. P. Sarachik and T. M. Klapwijk, Phys. Rev. B 71, 033312 (2005).