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

TL;DR

This study investigates how valley effects influence fractional quantum Hall states in an ultraclean SiGe/Si/SiGe two-dimensional electron system, revealing level merging and valley-dependent phenomena.

Contribution

It provides new insights into valley effects on composite fermion levels and fractional quantum Hall states in a bivalley SiGe/Si/SiGe system.

Findings

Minima at p=1, 2, 4, 6 observed in resistance

Disappearance of p=3 minimum below certain density

Resistance minimum at ν=3/5 independent of tilt angle

Abstract

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 $\nu=3/5$ 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.