Fractional Quantum Hall Effect in SiGe/Si/SiGe Quantum Wells in Weak Quantizing Magnetic Fields

TL;DR

This study experimentally investigates the fractional quantum Hall effect in SiGe/Si/SiGe quantum wells under weak magnetic fields, revealing composite fermion behavior, valley level interactions, and potential second-generation composite fermion formation.

Contribution

It provides new experimental insights into FQHE in SiGe/Si/SiGe quantum wells at weak magnetic fields, highlighting valley interactions and second-generation composite fermions.

Findings

Observation of FQHE minima at multiple composite fermion quantum numbers

Disappearance of certain minima below 7 Tesla due to valley level interactions

Detection of resistance minima at specific filling factors suggesting second-generation composite fermions

Abstract

We have experimentally studied the fractional quantum Hall effect (FQHE) in SiGe/Si/SiGe quantum wells in relatively weak magnetic fields, where the Coulomb interaction between electrons exceeds the cyclotron splitting by a factor of a few XX. Minima of the longitudinal resistance have been observed corresponding to the quantum Hall effect of composite fermions with quantum numbers $p$ = 1, 2, 3, and 4. Minima with $p$ = 3 disappear in magnetic fields below 7 Tesla, which may be a consequence of the intersection or even merging of the quantum levels of the composite fermions with different orientations of the pseudo-spin, i.e., those belonging to different valleys. We have also observed minima of the longitudinal resistance at filling factors $\nu$ = 4/5 and 4/11, which may be due to the formation of the second generation of the composite fermions.