Temperature Dependence of Valley Dynamics in a Six-fold Degenerate Si-(111) 2DEG

Using a two-dimensional electron gas (2DEG) on hydrogen terminated Si-(111) surfaces, we have studied magnetic field dependent valley dynamics of this six-fold degenerate system [1]. High field (up to 12 T) magneto-transport measurements indicate field-dependent valley splitting from the nominally six-fold degenerate system. In a simple non-interacting picture, one would expect no odd filling factors; although crystal misorientation and strain can lead to $\nu=2$ and 4, no such mechanism exists for $\nu=1,3,5$ [2]. Our samples show easily resolvable filling factors of, amongst others, 3 and 5, as well as filling factor dependent resistance anisotropies which indicate possible many-body effects beyond the simple interaction-free model. I will show activation measurements of these filling factors, discuss the stability of the resulting energy gaps, and consider potential causes of the splitting. A comparison of these activation measurements across different densities ($n_s=3 - 8 \times 10^{11}$ cm$^{-2}$) and samples of varying mobility ($10,000 - 100,000$ cm$^2/$Vs) will also be made. [1] R. N. McFarland et al., {\it Phys.~Rev.~B} {\bf 80} 161310R (2009), [2] K. Eng, R. N. McFarland, and B. E. Kane, Phys. Rev. Lett. 99, 016801 (2007)