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

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.