Paired states at 5/2: PH Pfaffian and particle-hole symmetry breaking

TL;DR

This paper investigates how particle-hole symmetry breaking via a mass term in Dirac composite fermions influences the emergence of PH Pfaffian and Pfaffian states, revealing conditions for their stability and instabilities.

Contribution

It introduces a detailed analysis of PH Pfaffian pairing in Dirac composite fermions with mass terms, extending previous models to include Landau level mixing effects.

Findings

Small Dirac mass leads to anti-Pfaffian or Pfaffian instability depending on sign.

Large mass induces PH Pfaffian-like instability regardless of sign.

Signatures of pairing observed at finite frequencies in RPA and hydrodynamic approaches.

Abstract

We study Cooper pairing in the Dirac composite fermion (CF) system. The presence of the mass term in the Dirac CF description (which may simulate Landau level mixing) i.e. breaking of particle-hole (PH) symmetry in this system, is a necessary condition for the existence of a PH Pfaffian-like topological state. In the scope of RPA approximation and hydrodynamic approach, we find some signatures of pairing at finite frequencies. Motivated by this insight, we extend our analysis to the case of a different but still Dirac quasi-particle (CF) representation, appropriate in the presence of a mass term, and discuss the likelihood of PH Pfaffian pairing and Pfaffian pairing in general. On the basis of gauge field effects, we find for small Dirac mass anti-Pfaffian or Pfaffian instability depending on the sign of mass, while for large mass (Landau level mixing), irrespective of its sign, PH Pfaffian-like instability.