On ground states of interacting Composite Fermions with spin at half filling

TL;DR

This paper investigates the ground states of interacting composite fermions with spin at half filling, revealing a competition between particle-particle and particle-hole pairing states influenced by interaction range and strength.

Contribution

It introduces a theoretical analysis of spinful composite fermions at half filling, showing how gauge fluctuations induce attractive interactions leading to different pairing ground states.

Findings

Particle-particle pairing favored at weak long-range Coulomb interactions.

Crossover from particle-particle to particle-hole pairing with increasing interaction strength.

Short-range interactions favor only particle-particle pairing.

Abstract

The effects of interactions in a 2D electron system in a strong magnetic field of two degenerate Landau levels with opposite spins and at filling factors 1/2 are studied. Using the Chern-Simons gauge transformation, the system is mapped to Composite Fermions. The fluctuations of the gauge field induce an effective interaction between the Composite Fermions which can be attractive in both the particle-particle and in the particle-hole channel. As a consequence, a spin-singlet (s-wave) ground state of Composite Fermions can exist with a finite pair-breaking energy gap for particle-particle or particle-hole pairs. The competition between these two possible ground states is discussed. For long-range Coulomb interaction the particle-particle state is favored if the interaction strength is small. With increasing interaction strength there is a crossover towards the particle-hole state. If the interaction is short range, only the particle-particle state is possible.