Valley Degenerate 2D Electrons in the Lowest Landau Level

TL;DR

This study investigates valley degeneracy and fractional quantum Hall effects in high-mobility 2D electrons on Si(111), revealing valley degeneracy, quantum Hall states, and composite fermion behavior with detailed energy estimates.

Contribution

It provides new insights into valley degeneracy and fractional quantum Hall states in Si(111) 2D electrons, including composite fermion formation and energy measurements.

Findings

Observation of six-fold valley degeneracy at low fields

Quantum Hall effect at all filling factors ≤6

Extended fractional quantum Hall hierarchy near ν=3/2

Abstract

We report low temperature magnetotransport measurements on a high mobility (\mu=325,000 cm^2/V sec) 2D electron system on a H-terminated Si(111) surface. While low magnetic field data indicate a six-fold valley degenerate system, we observe the integral quantum Hall effect at all filling factors \nu<=6 and find that \nu=2 develops in an unusually narrow temperature range. An extended, exclusively even numerator, fractional quantum Hall hierarchy occurs surrounding \nu=3/2, consistent with two-fold valley-degenerate composite fermions (CFs). We determine activation energies and estimate the CF mass.