Three-dimensional (3D) topological insulators (TI) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet Fe78Ga13B9 (FeGaB) and 3D TI Bi85Sb15 (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. The spin pumping parameters derived from inverse spin Hall effect (ISHE) measurements are consistent with the results of femtosecond light-pulse induced THz emission. These measurements are successfully verified using theoretical calculations of thickness-dependent spin Hall conductivity of BiSb thin films based on a tight-binding model.
Self-assembled InAs Quantum Dots (QDs) are often called “artificial atoms" and have long been of interest as components of quantum photonic and spintronic devices. Although there has been substantial progress in demonstrating optical control of both single spins confined to a single QD and entanglement between two separated QDs, the path toward scalable quantum photonic devices based on spins remains challenging. Quantum Dot Molecules, which consist of two closely-spaced InAs QDs, have unique properties that can be engineered with the solid state analog of molecular engineering in which the composition, size, and location of both the QDs and the intervening barrier are controlled during growth. Moreover, applied electric, magnetic, and optical fields can be used to modulate, in situ, both the spin and optical properties of the molecular states. We describe how the unique photonic properties of engineered Quantum Dot Molecules can be leveraged to overcome long-standing challenges to the creation of scalable quantum devices that manipulate single spins via photonics.
We experimentally compare the performance and image contrast of spontaneous Raman and coherent Stokes Raman scattering microscopy. We demonstrate the differences between these techniques on a series of geometry-controlled samples that range in complexity from a point (array of tips) to one-dimensional (line grating) and, lastly, two-dimensional (checkereboard) microstructure. Through the use of this sample series, a comparison of the focal volume, achievable signal-to-noise, and resulting image contrast is made. The results demonstrate the effciency and spatial resolution attainable in coherent Raman microscopy relative to spontaneous Raman microscopy. Additionally, we detail potential complications in the interpretation of coherent Raman images of sample fine structure, where contrast is no longer based solely on oscillator concentration but can be influenced by sample microstructure.
We exploit atomistic tight-binding theory to describe the effects of dot size, composition, internal strain and applied
strain on the confined states in nanocrystals and quantum dots. Both types of strain are critical, so we include the local
strain and the externally imposed strain on an equal footing via an atomistic valence force field approach. A tightbinding
model including an sp3s*d5 orbital model and spin-orbit effects is used. Several examples are discussed,
including GaAs nanocrystals, InP nanocrystals under pressure, and core-shell nanocrystals, to highlight the importance
of using atomistic models, extending tight-binding models to include d states, and having both internal and applied
strain.
Collective oscillations of valence electrons in metallic materials determine their optical response. The energy and
strength of these surface oscillations are a function of the shape, size and coupling of the nanoparticles. With the use of a
boundary element method (BEM), we solve Maxwell's equations to calculate light scattering and surface modes in
nanorods that are commonly used as hosts and/or samples in different field-enhanced scanning-probe microscopies and
spectroscopies. We calculate the near-field and far-field response of nanorods and show that different geometrical
terminations of the rods give different optical response in the far field for short rod lengths. For longer lengths, the
response of rods with different terminations becomes more similar. The near field features of the ends become most
evident close to the rod structural features that define the end capping. We identify four regimes for the separation
between nanorod pairs that provide different coupling between nanorods. We also show that the size dependence of the
nanorod response is characterized by a rod radius that gives a minimum wavelength for the dipolar response. For thicker
and thinner rods, the response redshifts.
A new equation for self-focusing of extremely focused intense pulses is derived. This method can be generalized to derive propagation equations for intense focused pulses to all orders of diffraction and dispersion with nonlinearity present, including the self-consistent derivation of nonlinear derivative coupling terms. This generalizes both the previously formulation of linear optical pulse propagation to the nonlinear propagation regime, and the cw nonlinear regime to the pulsed regime by including temporal characteristics of the pulse. Here we present the results for isotropic Kerr-type nonlinear media.
We theoretically investigate three approaches to trapping atoms above linear integrated optical waveguides. A two- color scheme balances the decaying evanescent elds of red- and blue-detuned light to produce a potential minimum above the guide. A one-color surface trap proposal uses blue-detuned light and the attractive surface interaction to provide a potential minimum. A third proposal uses blue-detuned light in two guides positioned above and below one another. The atoms are con ned to the \dark" spot in the vacuum gap between the guides. We nd that all three approaches can be used in principle to trap atoms in two- or three-dimensions with a few 10's of mW of laser power. Of these three methods, we show that the dark spot guide is the most robust to power fluctuations and provides the most viable design approach to constructing integrated optical circuits that could transport and manipulate atoms in a controlled manner.
KEYWORDS: Near field scanning optical microscopy, Glasses, Near field optics, Image acquisition, Cladding, Image processing, Gold, Particles, Nanoparticles, Image transmission
Near-field scanning optical microscopy (NSOM) is begin studied to achieve optical resolution much better than the diffraction limit. Improved resolution is realized when the sample is in the near field of the probe. Strong near-field coupling between sample and probe complicates image analysis. Experiments with well characterized tips and simple samples are needed to produce basic NSOM images. Detailed modeling able to reproduce imags and identify essential features in image formation is required. We analyze experimental NSOM transmission images of nanochannel glass arrays and of Au nanoparticles obtained in illumination mode. We use several approaches, including the discrete dipole method and the transfer matrix method, to simulate these images. Experimental and simulated images are compared to identify the contributions of tip-field structure, sample scattering, and the collection process to the images and to provide a clear interpretation of these NSOM images.
Electric field modulated spectra obtained from heterojunction samples have oscillatory structure that depends not only on the magnitude of the applied field but on confinement near the heterojunctions as well. Experiments indicate two field regions, each with distinct spectral lineshapes. Spectra obtained with relatively small dc electric fields have rapid oscillatory structure whose period does not significantly depend on the magnitude of the applied field. In contrast, the period of the bulk Franz-Keldysh oscillations that emerge with large field does. Theoretical calculations suggest that a crossover from the low to high field behavior occurs when carriers can freely move through the crystal.
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