Valley effects on the fractions in an ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

We observe minima of the longitudinal resistance corresponding to the quantum Hall effect of composite fermions at quantum numbers p = 1, 2, 3, 4, and 6 in an ultraclean strongly interacting bivalley SiGe/Si/SiGe two-dimensional electron system. The minima at p = 3 disappear below a certain electron density, although the surrounding minima at p = 2 and p = 4 survive at significantly lower densities. Furthermore, the onset for the resistance minimum at a filling factor v = 3/5 is found to be independent of the tilt angle of the magnetic field. These surprising results indicate the intersection or merging of the quantum levels of composite fermions with different valley indices, which reveals the valley effect on fractions.

Automated summary

In an ultraclean strongly interacting bivalley SiGe/Si/SiGe two-dimensional electron system, minima of longitudinal resistance corresponding to the quantum Hall effect of composite fermions are observed at different quantum numbers p = 1, 2, 3, 4, and 6. The disappearance of the minimum at p = 3 below a certain electron density, while the surrounding minima at p = 2 and p = 4 survive at significantly lower densities, suggests the intersection or merging of quantum levels of composite fermions with different valley indices, revealing the valley effect on fractions.