Composite fermion mass: Experimental measurements in ultrahigh quality two-dimensional electron systems

Composite fermions (CFs), exotic quasiparticles formed by pairing an electron and an even number of magnetic flux quanta, emerge at high magnetic fields in an interacting electron system, and can explain phenomena such as the fractional quantum Hall state (FQHS) and other many-body phases. CFs possess an effective mass (m(CF)) whose magnitude is inversely related to the most fundamental property of a FQHS, namely its energy gap. We present here experimental measurements of m(CF) in ultrahigh quality two-dimensional electron systems confined to GaAs quantum wells of varying thickness. An advantage of measuring m(CF) over gap measurements is that mass values are insensitive to disorder and are therefore ideal for comparison with theoretical calculations, especially for high-order FQHS. Our data reveal that m(CF) increases with increasing well width, reflecting a decrease in the energy gap as the electron layer becomes thicker and the in-plane Coulomb energy softens. Comparing our measured masses with available theoretical results, we find significant quantitative discrepancies, highlighting that more rigorous and accurate calculations are needed to explain the experimental data.

Automated summary

Composite fermions (CFs), formed by pairing an electron and an even number of magnetic flux quanta, are exotic quasiparticles that emerge in an interacting electron system at high magnetic fields. They can explain phenomena such as fractional quantum Hall state and other many-body phases. This study presents experimental measurements of the effective mass of CFs in GaAs quantum wells of varying thickness, revealing a relationship between mass and energy gap. Comparisons with theoretical calculations show significant discrepancies, indicating the need for more accurate calculations to explain the experimental data.