The Two-flux Composite Fermion Series of Fractional Quantum Hall States in Strained Si

TL;DR

This study investigates fractional quantum Hall states in strained silicon, revealing new states and insights into composite fermion degeneracy and valley splitting at very low temperatures and high magnetic fields.

Contribution

It reports the first observation of certain fractional quantum Hall states in Si/SiGe systems and analyzes the degeneracy lifting and valley splitting of composite fermions.

Findings

Observation of FQHE states at ν=2/3, 3/5, 4/7, 4/9, 2/5, 1/3 in strained Si

First detection of ν=1/3, 4/7, 4/9 states in Si/SiGe

Valley splitting estimated at ~1K

Abstract

Magnetotransport properties are investigated in a high-mobility two-dimensional electron system in the strained Si quantum well of a (100) Si_0.75Ge_0.25/Si/Si_0.75Ge_0.25 heterostructure, at temperatures down to 30mK and in magnetic fields up to 45T. We observe around \nu=1/2 the two-flux composite fermion (CF) series of the fractional quantum Hall effect (FQHE) at \nu=2/3, 3/5, 4/7, and at \nu=4/9, 2/5, 1/3. Among these FQHE states, the \nu=1/3, 4/7 and 4/9 states are seen for the first time in the Si/SiGe system. Interestingly, of the CF series, the 3/5 state is weaker than the nearby 4/7 state and the 3/7 state is conspicuously missing, resembling the observation in the integer quantum Hall effect regime that the \nu=3 is weaker than the nearby \nu=4 state. Our data indicate that the two-fold degeneracy of the CFs is lifted and an estimated valley splitting of ~1K.