Phases of correlated spinless fermions on the honeycomb lattice

TL;DR

This study investigates how strong interactions and quantum fluctuations influence phases of spinless fermions on a honeycomb lattice, revealing that quantum fluctuations prevent the quantum Hall phase and lead to a direct transition to a charge-modulated phase.

Contribution

It provides a detailed analysis of the phase transitions and the role of quantum fluctuations in spinless fermions on the honeycomb lattice using exact diagonalization and cluster perturbation theory.

Findings

Quantum fluctuations are significant at all interaction strengths.

Weak second-neighbor Coulomb repulsion favors a quantum anomalous Hall phase.

Quantum fluctuations prevent the formation of a stable quantum Hall phase.

Abstract

We use exact diagonalization and cluster perturbation theory to address the role of strong interactions and quantum fluctuations for spinless fermions on the honeycomb lattice. We find quantum fluctuations to be very pronounced both at weak and strong interactions. A weak second-neighbor Coulomb repulsion $V_2$ induces a tendency toward an interaction-generated quantum anomalous Hall phase, as borne out in mean-field theory. However, quantum fluctuations prevent the formation of a stable quantum Hall phase before the onset of the charge-modulated phase predicted at large $V_2$ by mean-field theory. Consequently, the system undergoes a direct transition from the semimetal to the charge-modulated phase. For the latter, charge fluctuations also play a key role. While the phase, which is related to pinball liquids, is stabilized by the repulsion $V_2$, the energy of its low-lying charge excitations scales with the electronic hopping $t$, as in a band insulator.