Quantum magnetism of topologically-designed graphene nanoribbons

Abstract

Based on the Hubbard models, quantum magnetism of topologically-designed graphene nanoribbons (GNRs) is studied using exact numerical simulations. We first study a two-band Hubbard model describing the low-energy topological bands using density matrix renormalization group (DMRG) and determinant quantum Monte Carlo (DQMC) methods. It is found the spin correlations decay quickly with the distance, and the local moment is extrapolated to zero in the presence of symmetry-breaking terms. The results show that the two-band Hubbard chain is nonmagnetic, which is in contrast to the mean-field calculation predicting a critical interaction for the magnetic transition. We then include the Hubbard interaction to the topological-designed GNRs. For large interactions, the spin correlations keep finite for all distances, and the magnetic order develops. The local moment is extrapolated to almost zero for weak interactions, and begins to increase rapidly from a critical interaction. The estimated critical value is much larger than the realistic value in graphene, and we conclude the experimentally relevant GNRs is nonmagnetic, which is consistent with the experimental results.

Engineering plasmon modes and their loss in armchair graphene nanoribbons by selected edge-extended defects

“…Therefore, special attention has been directed toward the * Author to whom any correspondence should be addressed. edge-modified armchair graphene nanoribbons (AGNRs) because of their versatility, stability and interesting physics, e.g., topological behavior [17,18], band engineering [2], quantum-phase transition [19], and quantum magnetism [20].…”

“…Moreover, the band structures and charge-density distributions of various types of edge-modified AGNRs were analyzed in reference [19] by employing first-principles computations and the tight-binding model along with scanning-tunnelingspectroscopy measurements. Additionally, the quantum magnetism of topologically-designed GNRs was evaluated numerically based on the Hubbard model [20]. Furthermore, a study of the charge-transport mechanism of GNRs was conducted in reference [45] based on a semi-classical model with the tight-binding approximation.…”

Engineering plasmon modes and their loss in armchair graphene nanoribbons by selected edge-extended defects

“…Edge defects, which usually appear during the fabrication processes for GNRs, have been shown to modify the fundamental characteristics of targeted materials. Therefore, special attention has been directed toward the edge-modified armchair graphene nanoribbons (AGNRs) because of their versatility, stability and interesting physics, e.g., topological behavior [17,18], band engineering [2], quantum-phase transition [19], and quantum magnetism [20].…”

“…Edge defects, which usually appear during the fabrication processes for GNRs, have been shown to modify the fundamental characteristics of targeted materials. Therefore, special attention has been directed toward the edge-modified armchair graphene nanoribbons (AGNRs) because of their versatility, stability and interesting physics, e.g., topological behavior [17,18], band engineering [2], quantum-phase transition [19], and quantum magnetism [20].Collective excitation in a quantum many-body system becomes a critical concept for a deep understanding of the physical properties of materials, such as the optical-absorption spectra [21], fractional-quantum Hall plateaus [22], electronic excitations [23] and decay rates [24,25], to name just a few. In this paper, we will concentrate on plasmons, which result from collective excitations of Coulomb-coupled charged carriers in the conduction or valence bands, and their various effects as well.…”

“…[19] by employing first-principles computations and the tight-binding model along with scanning-tunneling-spectroscopy measurements. Additionally, the quantum magnetism of topologically-designed GNRs was evaluated numerically based on the Hubbard model [20]. Furthermore, a study of the charge-transport mechanism of GNRs was conducted in Ref.…”