Nicholas Pike

Tight-Binding Model for Adatoms on Graphene: Analytical Density of States, Spectral Function, and Induced Magnetic Moment

In the limit of low adatom concentration, we obtain exact analytic expressions for the local and total density of states (LDOS, TDOS) for a tight-binding model of adatoms on graphene. The model is not limited to nearest-neighbor hopping but can include hopping between carbon atoms at any separation. We also find an analytical expression for the spectral function A(k,E) of an electron of Bloch vector k and energy E on the graphene lattice, to first order in the adatom concentration. We treat the electron-electron interaction by including a Hubbard term on the adatom, which we solve within a mean-field approximation. For finite Hubbard U ,w e find the spin-polarized LDOS, TDOS, and spectral function self-consistently. For any choice of parameters of the tight-binding model within mean-field theory, we find a critical value of U above which a moment develops on the adatom. Preliminary calculations also indicate that this moment can be switched on and off by varying the Fermi energy. For most choices of parameters, we find a substantial charge transfer from the adatom to the graphene host.

Origin of the counterintuitive dynamic charge in the transition metal dichalcogenides

We investigate the chemical bonding characteristics of the transition metal dichalcogenides based on their static and dynamical atomic charges within Density Functional Theory. The dynamical charges of the trigonal transition metal dichalcogenides are anomalously large, while in their hexagonal counterparts, their sign is even counterintuitive i.e. the transition metal takes the negative charge. This phenomenon cannot be understood simply in terms of a change in the static atomic charge as it results from a local change of polarization. We present our theoretical understanding of these phenomena based on the perturbative response of the system to a static electric field and by investigating the hybridization of the molecular orbitals near the Fermi level. Furthermore, we establish a link between the sign of the Born effective charge and the

Plasmonic waves on a chain of metallic nanoparticles: effects of a liquid-crystalline host

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Model for the spin-dependent Seebeck coefficient of InSb in a magnetic field

-backbonding in organic chemistry and propose an experimental procedure to verify the calculated sign of the dynamical charge in the transition metal dichalcogenides.

Faraday rotation, band splitting, and one-way propagation of plasmon waves on a nanoparticle chain

A chain of metallic particles, of sufficiently small diameter and spacing, allows linearly polarized plasmonic waves to propagate along the chain. In this paper, we consider how these waves are altered when the host is a nematic or cholesteric liquid crystal (NLC or CLC). In an NLC host, with the principal axis (director) oriented either parallel or perpendicular to the chain, we find that the dispersion relations of both the longitudinal (L) and transverse (T) modes are significantly altered relative to those of an isotropic host. Furthermore, when the director is perpendicular to the chain, the doubly degenerate T branch is split into two nondegenerate linearly polarized branches by the anisotropy of the host material. In a CLC liquid crystal with a twist axis parallel to the chain, the two T branches are again found to be split, but are no longer linearly polarized; the dispersion relations depend on the cholesteric pitch angle. To illustrate these results, we calculate the L and T dispersion relations for both types of liquid crystals, assuming that the metal is described by a Drude dielectric function. The formalism can, in principle, include single-particle damping and could be generalized to include radiation damping. The present work suggests that the dispersion relations of plasmonic waves on a chain of nanoparticles can be controlled by immersing the chain in an NLC or a CLC and varying the director axis or pitch angle by applying suitable external fields.

Electron-Beam Manipulation of Silicon Dopants in Graphene

We develop a simple theory for the longitudinal spin Seebeck effect in n-doped InSb in an external magnetic field. We consider spin-

Graphene with adatoms: Tuning the magnetic moment with an applied voltage

1/2

Theory of plasmonic waves on a chain of metallic nanoparticles in a liquid crystalline host

electrons in the conduction band of InSb with a temperature gradient parallel to the applied magnetic field. In the absence of spin-orbit interactions, a Boltzmann equation approach leads to a spin current parallel to the field and proportional to the temperature gradient. The calculated longitudinal spin Seebeck coefficients oscillates as a function of magnetic field B; the peak positions are approximately periodic in 1/B. The oscillations arise when the Fermi energy crosses the bottom of a Landau band.

Spin waves on chains of YIG particles: dispersion relations, Faraday rotation, and power transmission

We calculate the dispersion relations of plasmonic waves propagating along a chain of semiconducting or metallic nanoparticles in the presence of both a static magnetic field B and a liquid crystalline host. The dispersion relations are obtained using the quasistatic approximation and a dipole-dipole approximation to treat the interaction between surface plasmons on different nanoparticles. For plasmons propagating along a particle chain in a nematic liquid crystalline host with both B and the director parallel to the chain, we find a small, but finite, Faraday rotation angle. For B perpendicular to the chain, but director still parallel to the chain, the field couples the longitudinal and one of the two transverse plasmonic branches. This coupling is shown to split the two branches at the zero field crossing by an amount proportional to |B|. In a cholesteric liquid crystal host and an applied magnetic field parallel to the chain, the dispersion relations for left- and right-moving waves are found to be d...

Vibrational and dielectric properties of the bulk transition metal dichalcogenides

The direct manipulation of individual atoms in materials using scanning probe microscopy has been a seminal achievement of nanotechnology. Recent advances in imaging resolution and sample stability have made scanning transmission electron microscopy a promising alternative for single-atom manipulation of covalently bound materials. Pioneering experiments using an atomically focused electron beam have demonstrated the directed movement of silicon atoms over a handful of sites within the graphene lattice. Here, we achieve a much greater degree of control, allowing us to precisely move silicon impurities along an extended path, circulating a single hexagon, or back and forth between the two graphene sublattices. Even with manual operation, our manipulation rate is already comparable to the state-of-the-art in any atomically precise technique. We further explore the influence of electron energy on the manipulation rate, supported by improved theoretical modeling taking into account the vibrations of atoms near the impurities, and implement feedback to detect manipulation events in real time. In addition to atomic-level engineering of its structure and properties, graphene also provides an excellent platform for refining the accuracy of quantitative models and for the development of automated manipulation.