Composite fermions in graphene fractional quantum Hall state at half filling: evidence for Dirac composite fermions

TL;DR

This paper provides experimental evidence that composite fermions in graphene at half filling behave as Dirac particles, showing weak antilocalization and a logarithmic temperature dependence of conductivity, confirming their relativistic nature.

Contribution

The study demonstrates that composite fermions in graphene are Dirac particles at half filling, supporting the Dirac composite fermion theory in a high-mobility graphene system.

Findings

Weak temperature dependence of conductivity at half filling.

Logarithmic quantum correction consistent with Dirac fermions.

Evidence of weak antilocalization indicating relativistic behavior.

Abstract

Composite fermions in fractional quantum Hall (FQH) systems are believed to form a Fermi sea of weakly interacting particles at half filling $\nu=1/2$. Recently, it was proposed (D. T. Son, Phys. Rev. X 5, 031027 (2015)) that these composite fermions are Dirac particles. In our work, we demonstrate experimentally that composite fermions found in monolayer graphene are Dirac particles at half filling. Our experiments have addressed FQH states in high-mobility, suspended graphene Corbino disks in the vicinity of $\nu=1/2$. We find strong temperature dependence of conductivity $\sigma$ away from half filling, which is consistent with the expected electron-electron interaction induced gaps in the FQH state. At half filling, however, the temperature dependence of conductivity $\sigma(T)$ becomes quite weak as expected for a Fermi sea of composite fermions and we find only logarithmic dependence of $\sigma$ on $T$. The sign of this quantum correction coincides with weak antilocalization of composite fermions, which reveals the relativistic Dirac nature of composite fermions in graphene.