Dirac Fermion Hierarchy of Composite Fermi Liquids

TL;DR

This paper explores the properties of composite Fermi liquids at various filling fractions, revealing a uniform Berry curvature distribution and proposing a generalized Dirac fermion theory with internal gauge flux attachment.

Contribution

It extends Son's Dirac fermion theory from half filling to all relevant fillings by incorporating internal gauge flux attachment, supported by numerical evidence.

Findings

Berry curvature is uniformly distributed over the Fermi sea except at the center.

An additional π phase is observed at the Fermi sea center.

Numerical results support the generalized theory with internal gauge flux attachment.

Abstract

Composite Fermi liquids (CFLs) are compressible states that can occur for 2D interacting fermions confined in the lowest Landau level at certain Landau level fillings. They have been understood as Fermi seas formed by composite fermions which are bound states of electromagnetic fluxes and electrons as reported by Halperin, Lee and Read [Phys. Rev. B 47, 7312 (1993)]. At half filling, an explicitly particle-hole symmetric theory based on Dirac fermions was proposed by Son [Phys. Rev. X 5, 031027 (2015)] as an alternative low energy description. In this work, we investigate the Berry curvature of CFL model wave functions at a filling fraction one-quarter, and observe that it is uniformly distributed over the Fermi sea except at the center where an additional $\pi$ phase was found. Motivated by this, we propose an effective theory which generalizes Son's half filling theory, by internal gauge flux attachment, to all filling fractions in which fermionic CFLs can occur. The numerical results support the idea of internal gauge flux attachment.