Details of a theoretical model for electronic structure of the diamond vacancies (original) (raw)
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Generalized Hubbard model for many-electron states of the diamond vacancies: A non-CI approach
Physica Status Solidi B-basic Solid State Physics, 2006
Many-electron calculations based on a generalized Hubbard Hamiltonian for electronic states of the diamond vacancies are reported. The model does not use the configuration interaction (CI) method and proper tetrahedral symmetry and spin properties of the defect are included in the Hamiltonian. Atomic orbital bases are introduced for the Hamiltonian calculation. Excited states of both neutral and negatively charged vacancies in diamond are calculated. The calculated values for the experimentally observed first dipole transition energies of the vacancies in diamond, GR1 and ND1 bands, are in good agreement with experiment. To obtain these results, we used a semi-empirical Hamiltonian parameter. The position of the low-lying 3T 1 state was found to be 260 meV above the ground state, which is consistent with experimental expectations. In addition to the energy spectrum, the model gives all eigenfunctions of the vacancies, which have not been calculated before. This model has high potential for further applications in point defects of diamond and other semiconductors.
Electronic structure of the nitrogen-vacancy center in diamond from first-principles theory
Physical Review B, 2008
The nitrogen-vacancy ͑NV͒ center is a paramagnetic defect in diamond with applications as a qubit. Here, we investigate its electronic structure by using ab initio density functional theory for five different NV center models of two different cluster sizes. We describe the symmetry and energetics of the low-lying states and compare the optical frequencies obtained to experimental results. We compute the major transition of the negatively charged NV centers to within 25-100 meV accuracy and find that it is energetically favorable for substitutional nitrogens to donate an electron to NV 0. The excited state of the major transition and the NV 0 state with a neutral donor nitrogen are found to be close in energy.
Simulations of large multi-atom vacancies in diamond
Diamond and Related Materials, 2010
We generated and evaluated energetically a very large number of vacancy V n clusters representing nanosize voids or cavities in diamond for n up to 14 using a new generational algorithm. We evaluated the relaxed geometries and energies of these contiguous vacancy clusters using a tight binding density functional theory (TBDFT). For up to n = 7 we generated all possible structures and evaluated their relaxed geometries. For n = 8 through n = 14 we selectively generated a large number of vacancy clusters and obtained highly stable structures and their energies. By analyzing the energy levels and the corresponding orbitals, we identified the surface states of the voids and their symmetries. Significant differences with respect to vacancy clusters in silicon were found. The results were interpreted by finding that certain structures become relatively more stable due to a process we call local graphitization, which can be identified by a tetrahedron of graphitization (TOG), and it can be characterized by elongation of certain carbon-carbon contacts and by the concomitant appearance of new states in the gap. The beginning of graphitization, as indicated by geometrical and energetic descriptors in small stable vacancy clusters, may have a role in the formation mechanisms of various sp 2 hybridized structures in carbons.
European Physical Journal B, 2008
The relationship between unpaired electron delocalization and nearest-neighbor atomic relaxations in the vacancies of diamond has been determined in order to understand the microscopic reason behind the neighboring atomic relaxation. The Density Functional Theory (DFT) cluster method is applied to calculate the single-electron wavefunction of the vacancy in different charge states. Depending on the charge and spin state of the vacancies, at outward relaxations, 84-90% of the unpaired electron densities are localized on the first neighboring atoms. The calculated spin localizations on the first neighboring atoms in the ground state of the negatively charged vacancy and in the spin quintet excited state of the neutral vacancy are in good agreement with Electron Paramagnetic Resonance (EPR) measurements. The calculated spin localization of the positively charged vacancy contrasts with the tentative assignment of the NIRIM-3 EPR signal to this center in (p-type) semiconductor diamond. The sign of the lattice relaxation in the diamond vacancy is explained based on the effect of electron delocalization on nearest-neighbor ion-ion screening, and also its effect on the bond length of neighboring atoms.
Quantum mechanical modeling of the structure and doping properties of defects in diamond
2005
The extreme materials properties of diamond lend it to a range of semiconductor applications, but the difficulty in forming n-type diamond, and the unintentional inclusion of deleterious impurities has proved problematic. Co-doping diamond with boron and deuterium yields n-type conduction and recent theory suggests that BD2 and BD3 complexes have shallow donor levels. We show here that the proposed structures are unstable and structural relaxation result in deep levels or passive defects. We also comment on other proposed co-doping schemes: N-H-N, S-H and Si4-N. Finally we show that combination of theory and the polarized uptake of Ni in diamond contradict the current interstitial Ni models for the 1.404 eV center.
Properties of nitrogen-vacancy centers in diamond: the group theoretic approach
We present a procedure that makes use of group theory to analyze and predict the main properties of the negatively charged nitrogen-vacancy (NV) center in diamond. We focus on the relatively low temperatures limit where both the spin-spin and spin-orbit effects are important to consider. We demonstrate that group theory may be used to clarify several aspects of the NV structure, such as ordering of the singlets in the (e 2 ) electronic configuration, the spin-spin and the spin-orbit interactions in the (ae) electronic configuration. We also discuss how the optical selection rules and the response of the center to electric field can be used for spin-photon entanglement schemes. Our general formalism is applicable to a broad class of local defects in solids. The present results have important implications for applications in quantum information science and nanomagnetometry.
Nitrogen-vacancy center in diamond: Model of the electronic structure and associated dynamics
Physical Review B, 2006
Symmetry considerations are used in presenting a model of the electronic structure and the associated dynamics of the nitrogen-vacancy center in diamond. The model accounts for the occurrence of optically induced spin polarization, for the change of emission level with spin polarization and for new measurements of transient emission. The rate constants given are in variance to those reported previously.
Physical Review Letters, 2009
We report a study of the 3 E excited-state structure of single negatively-charged nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at cryogenic temperatures and optically detected magnetic resonance. A theoretical model is developed and shows excellent agreement with experimental observations. Besides, we show that the two orbital branches associated with the 3 E excited-state are averaged when operating at room temperature. This study leads to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing.
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
New Journal of Physics, 2011
The negatively charged nitrogen-vacancy centre is a unique defect in diamond that possesses properties highly suited to many applications, including quantum information processing, quantum metrology, and biolabelling. Although the unique properties of the centre have been extensively documented and utilised, a detailed understanding of the physics of the centre has not yet been achieved. Indeed there persists a number of points of contention regarding the electronic structure of the centre, such as the ordering of the dark intermediate singlet states. Without a detailed model of the centre's electronic structure, the understanding of the system's unique dynamical properties can not effectively progress. In this work, the molecular model of the defect centre is fully developed to provide a self consistent model of the complete electronic structure of the centre. The application of the model to describe the effects of electric, magnetic and strain interactions, as well as the variation of the centre's fine structure with temperature, provides an invaluable tool to those studying the centre and a means to design future empirical and ab initio studies of this important defect.