Interaction and excitonic insulating transition in graphene

TL;DR

This paper investigates how various screening effects influence the Coulomb-driven semimetal-insulator transition in graphene, revealing that screening suppresses the transition unless a strong contact interaction is present.

Contribution

It demonstrates that screening effects significantly suppress the excitonic transition in graphene and identifies conditions under which the transition can still occur.

Findings

Screening suppresses the transition beyond a critical threshold.

Contact four-fermion interactions can restore the transition.

Transition is suppressed by disorder, thermal fluctuations, doping, and finite volume.

Abstract

The strong long-range Coulomb interaction between massless Dirac fermions in graphene can drive a semimetal-insulator transition. We show that this transition is strongly suppressed when the Coulomb interaction is screened by such effects as disorder, thermal fluctuation, doping, and finite volume. It is completely suppressed once the screening factor $\mu$ is beyond a threshold $\mu_{c}$ even for infinitely strong coupling. However, such transition is still possible if there is an additional strong contact four-fermion interaction. The differences between screened and contact interactions are also discussed.