Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Phys Rev Lett. 2010 Jan 8;104(1):016805. doi: 10.1103/PhysRevLett.104.016805. Epub 2010 Jan 7.
We study a two-dimensional electron system where the electrons occupy two conduction band valleys with anisotropic Fermi contours and strain-tunable occupation. We observe persistent quantum Hall states at filling factors nu=1/3 and 5/3 even at zero strain when the two valleys are degenerate. This is reminiscent of the quantum Hall ferromagnet formed at nu=1 in the same system at zero strain. In the absence of a theory for a system with anisotropic valleys, we compare the energy gaps measured at nu=1/3 and 5/3 to the available theory developed for single-valley, two-spin systems, and find that the gaps and their rates of rise with strain are much smaller than predicted.
我们研究了一个二维电子系统，其中电子占据两个各向异性费米轮廓和应变可调的导带谷。当两个谷简并时，即使在零应变下，我们也观察到填充因子 nu=1/3 和 5/3 的稳定量子霍尔态。这让人联想到在零应变下相同系统中填充因子 nu=1 时形成的量子霍尔铁磁体。由于缺乏各向异性谷系统的理论，我们将在 nu=1/3 和 5/3 处测量的能隙与为单谷、双自旋系统开发的可用理论进行比较，并发现能隙及其随应变的上升速率比预期的小得多。
