Many-body Configuration Interaction Research Articles

Effects of interedge scattering on the Wigner crystallization in graphene nanoribbons

We investigate the effects of coupling between the two zigzag edges of graphene nanoribbons on the Wigner crystallization of electrons and holes using a combination of tight-binding, mean field Hubbard and many-body configuration interaction methods. We show that the thickness of the nanoribbon plays a crucial role in the formation of Wigner crystal. For ribbon widths smaller than 16 \mbox{\AA}, increased kinetic energy overcomes the long-range Coulomb repulsion and suppresses the Wigner crystallization. For wider ribbons up to 38 \mbox{\AA} wide, strong Wigner localization is observed for even number of electrons, revealing an even-odd effect also found in Coulomb blockade addition spectrum. Interedge correlations are found to be strong enough to allow simultaneous crystallization on both edges, although an applied electric field can decouple the two edges. Finally, we show that Wigner crystallization can also occurs for holes, albeit weaker than for electrons.

Wigner crystallization at graphene edges

Using many-body configuration interaction techniques we show that Wigner crystallization occurs at the zigzag edges of graphene at surprisingly high electronic densities up to $0.8$ $\mbox{nm}^{-1}$. In contrast with one-dimensional electron gas, the flat-band structure of the edge states makes the system interaction dominated, facilitating the electronic localization. The resulting Wigner crystal manifests itself in pair-correlation functions, and evolves smoothly as the edge electron density is lowered. We also show that the crystallization affects the magnetization of the edges. While the edges are fully polarized when the system is charge neutral (i.e. high density), above the critical density, the spin-spin correlations between neighboring electrons go through a smooth transition from antiferromagnetic to magnetic coupling as the electronic density is lowered.

Tuning Charge and Spin Excitations in Zigzag Edge Nanographene Ribbons

Graphene and its quasi-one-dimensional counterpart, graphene nanoribbons, present an ideal platform for tweaking their unique electronic, magnetic and mechanical properties by various means for potential next-generation device applications. However, such tweaking requires knowledge of the electron-electron interactions that play a crucial role in these confined geometries. Here, we have investigated the magnetic and conducting properties of zigzag edge graphene nanoribbons (ZGNRs) using the many-body configuration interaction (CI) method on the basis of the Hubbard Hamiltonian. For the half-filled case, the many-body ground state shows a ferromagnetic spin-spin correlation along the zigzag edge, which supports the picture obtained from one-electron theory. However, hole doping reduces the spin and charge excitation gap, making the ground state conducting and magnetic. We also provide a two-state model that explains the low-lying charge and spin excitation spectrum of ZGNRs. An experimental setup to confirm the hole-mediated conducting and magnetic states is discussed.

Electron-electron interactions on the edge states of graphene: A many-body configuration interaction study

We have studied zigzag and armchair graphene nanoribbons (GNRs), described by the Hubbard Hamiltonian using quantum many-body configuration interaction methods. Due to finite termination, we find that the bipartite nature of the graphene lattice gets destroyed at the edges, making the ground state of the zigzag GNRs a high spin state, whereas the ground state of the armchair GNRs remains a singlet. Our calculations of charge and spin densities suggest that, although the electron density prefers to accumulate on the edges (instead of spin polarization), the up and down spins prefer to mix throughout the GNR lattice. While the many-body charge gap results in insulating behavior for both kinds of GNRs, the conduction upon application of electric field is still possible through the edge channels because of their high electron density. Analysis of optical states suggest differences in quantum efficiency of luminescence for zigzag and armchair GNRs, which can be probed by simple experiments.

Density Matrix Renormalization Group Approach for Many-Body Open Quantum Systems

The density matrix renormalization group (DMRG) approach is extended to complex-symmetric density matrices characteristic of many-body open quantum systems. Within the continuum shell model, we investigate the interplay between many-body configuration interaction and coupling to open channels in case of the unbound nucleus (7)He. It is shown that the extended DMRG procedure provides a highly accurate treatment of the coupling to the nonresonant scattering continuum.

Theoretical predictions of the electronic and optical properties of single and coupled (In,Ga)As/GaAs quantum dots

We show how an atomistic pseudopotential plus many-body configuration interaction theory can address the main spectroscopic features of self-assembled dots including, excitons, trions, biexcitons, fine-structure, charging spectra as well as electric-field dependence of entanglement in dot molecules.

Conduction band satellite of Ni metal observed using 3p-3d resonant inverse photoemission study

Resonant inverse photoemission spectra of Ni metal have been obtained across the Ni 3$p$ absorption edge. The intensity of Ni 3$d$ band just above Fermi edge shows asymmetric Fano-like resonance. Satellite structures are found at about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the absorption edge. The satellite structures are due to a many-body configuration interaction and confirms the existence of 3$d^8$ configuration in the ground state of Ni metal.

Resonant inverse photoemission spectroscopy in soft X-ray region

Resonant inverse photoemission spectroscopy (RIPES) measurements have been performed in the soft X-ray (SX) region. The energy region, which could not be accessible up to these days, includes core levels of many important elements to be investigated. They were applied to transition metals (TM), rare earth (RE) metals, and their compounds. Remarkable resonance enhancement was observed in Ce 4d→4f resonance of some Ce compounds. This gives us complementary information with Ce 3d resonance IPES that was reported before. 2p and 3p resonance spectra were observed for the TM compounds. These resonances show rather weak enhancement compared with those of Ce compounds, although apparent resonance feature was observed. These results are well-reproduced by many-body configuration interaction on the basis of the Anderson impurity model. Though the study has just started, the results demonstrated the effectiveness of the RIPES measurements.

Resonant Inverse Photoemission and Many-Body Effect in Nickel

We calculate a resonant inverse photoemission spectroscopy (IPES) spectrum at the Ni 3 p core threshold (3 d n →3 p 5 3 d n +2 →3 d n +1 ), from a viewpoint of a many-body configuration interaction (CI), on the basis of the Anderson impurity model. The calculated IPES spectrum exhibits a single main peak just above the Fermi level E F under off-resonance, while it has a shoulder extending to 4 eV above E F under on-resonance conditions. Under on-resonance conditions, the main peak intensity shows a dip whose magnitude is a function of the incident electron energy e , while the shoulder is resonantly enhanced. The interference between the direct 3 d 8 →3 d 9 and resonant 3 d 8 →3 p 5 3 d 10 →3 d 9 processes and CI in both the initial and final states leads to the above result. Resonant IPES is therefore considered to be a promising method of directly determining whether a 3 d 8 configuration in the initial state, inferred by analysis of various high-energy spectroscopic data, does in fact exist. The main p...

Spin Polarization of 3d, 3pand 3sPhotoemission in Ferromagnetic Nickel Predicted at Ni 2pCore Threshold

We discuss the spin polarization of 3 d , 3 p and 3 s photoemission (PE) spectra at the Ni 2 p core threshold for ferromagnetic Ni from a view point of many-body configuration interaction (CI) on the basis of the Anderson impurity model including full atomic multiplets. The calculated relative spin polarization at the 6-eV satellite of 3 d PE, which is supposed to be a mixture of 1 G , 1 D and 3 P 3 d 8 multiplets, is, as a function of the incident photon energy (ω), shown to exhibit a remarkable dip in the 2 p 1/2 region, while not in the 2 p 3/2 region. The role of the core spin-orbit interaction in the intermediate state of the resonant photoemission, as a possible origin of the dip, is discussed. An expected spin polarization of 3 p and 3 s PE spectra at off- and on-resonances, including that for the circularly polarized incident light, is also discussed and the usefulness of it in identifying the character of the final state of the PE and in validating the CI approach in the present system is demonst...

Spin Polarization of 3dPhotoemission at 3pThreshold in Ferromagnetic Ni Expected from Configuration Interaction Model

We discuss the spin polarization of resonant 3 d photoemission spectra at the Ni 3 p threshold for ferromagnetic Ni from the viewpoint of a many-body configuration interaction, on the basis of the Anderson impurity model including atomic multiplets. The calculated relative spin polarization (majority-spin minus minority-spin divided by their sum) at the 6-eV satellite is shown to exhibit a dip structure with a minimum of ∼20% and a maximum of ∼35% separated by 7∼8 eV near on-resonance as a function of incident photon energy, which is consistent with the results of recent experiment. Its structure is, contrary to previous discussions, shown to be caused not only by the Fano interference effect but also by the 3 p -3 d exchange and 3 p spin-orbit interaction in the intermediate state of the second-order resonant process. The spin polarization in the main peak and in the various positions of satellites is also discussed.