Optical spin Hall effects in plasmonic chains

Observation of optical spin Hall effects (OSHEs) manifested by a spin-dependent momentum redirection is presented. The effect occurring solely as a result of the curvature of the coupled localized plasmonic chain is regarded as the locally isotropic OSHE, while the locally anisotropic OSHE arises from the interaction between the optical spin and the local anisotropy of the plasmonic mode rotating along the chain. A wavefront phase dislocation was observed in a circular curvature, in which the dislocation strength was enhanced by the locally anisotropic effect.     

Circular Dichroism Studies on Plasmonic Nanostructures

In recent years, optical chirality of plasmonic nanostructures has aroused great interest because of innovative fundamental understanding as well as promising potential applications in optics, catalysis and sensing. Herein, state‐of‐the‐art studies on circular dichroism (CD) characteristics of plasmonic nanostructures are summarized. The hybrid of achiral plasmonic nanoparticles (NPs) and chiral molecules is explored to generate a new CD response at the plasmon resonance as well as the enhanced CD intensity of chiral molecules in the UV region, owing to the Coulomb static and dynamic dipole interactions between plasmonic NPs and chiral molecules. As for chiral assembly of plasmonic NPs, plasmon–plasmon interactions between the building blocks are found to induce generation of intense CD response at the plasmon resonance. Three‐dimensional periodical arrangement of plasmonic NPs into macroscale chiral metamaterials is further introduced from the perspective of negative refraction and photonic bandgap. A strong CD signal is also discerned in achiral planar plasmonic nanostructures under illumination of circular polarized plane wave at oblique incidence or input vortex beam at normal incidence. Finally perspectives, especially on future investigation of time‐resolved CD responses, are presented.     

Three-dimensional chiral plasmonic oligomers

The living world is chiral. Chirality or the handedness of a structure or molecule is at the heart of life itself. Recently, it has been shown that plasmonic structures exhibit unprecedented and gigantic chiral optical responses. Here we show that truly three-dimensional arrangements of plasmonic "meta-atoms" only exhibit a chiral optical response if similar plasmonic "atoms" are arranged in a handed fashion as we require resonant plasmonic coupling. Moreover, we demonstrate that such particle groupings, similarly to molecular systems, possess the capability to encode their three-dimensional arrangement in unique and well-modulated spectra making them ideal candidates for a three-dimensional chiral plasmon ruler. Our results are crucial for the future design and improvement of plasmonic chiral optical systems, for example, for ultrasensitive enantiomer sensing on the single molecule level.     

Plasmonic resonance effects for tandem receiving-transmitting nanoantennas

A nanoplasmonic "transceiver" was assembled to examine the efficiency of coupled plasmonic antennas and their resonance interactions. In particular, plasmonic focusing receiver antenna coupled to transmitting annular antenna having a short central plasmonic wire was measured. The receiver collected incoming radially polarized light and efficiently focused and coupled it to a rear side transmitter comprised of a short resonant plasmonic wire and annular aperture. Transmission spectra exhibited a substantial signature of the wire Fabry-Perot resonances. The wire antenna crossection was improved by nearly 3 orders of magnitude by the focusing antenna system.     

Magnetic plasmon formation and propagation in artificial aromatic molecules

The plasmonic properties of coupled metallic nanostructures are understood through the analogy between their collective plasmon modes and the electronic orbitals of corresponding molecules. Here we expand this analogy to planar arrangements of plasmonic nanostructures whose magnetic plasmons directly resemble the delocalized orbitals of aromatic hydrocarbon molecules. The heptamer structure serves as a benzene-like building block for a family of plasmonic artificial aromatic analogs with fused ring structures. Antiphase magnetic plasmons are excited in adjacent fused heptamer units, which for a linear multiheptamer structure is a behavior controlled by the number of units in the structure. This antiphase coupling gives rise to plasmonic "antiferromagnetic" behavior in multiple repeated heptamer structures, supporting the propagation of low-loss magnetic plasmons in this new waveguide geometry.     

Semiconductor spintronics

We review recent progress made in the field of semiconductor spintronics, a branch of semiconductor electronics where both charge and spin degrees of freedom play an important role in realizing unique functionalities. We first describe the new spin-dependent phenomena found in semiconductors including carrier-induced ferromagnetism in III-V compounds, followed by an account of our current understanding of such spin-dependent phenomena. Then we summarize the challenges the semiconductor spintronics has to meet in order for it to be a success as "electronics".     

Electronic properties from analysis of the harmonic content of the de Haas-van Alphen effect: Application to dilute magnetic alloys

A new technique, third harmonic de Haas-van Alphen (dHvA) wave shape analysis, is described for measurement of the spin-dependent interactions between conduction electrons and local moments in dilute alloys. We derive expressions for the harmonic content of the dHvA effect in a general case, including simultaneous contributions due to (1) magnetic interaction (MI or Shoenberg effect), (2) the spin-dependent scattering (SDS) of conduction electrons, and (3) exchange energy shifts in their Landau levels due to local moments, in addition to the usual Lifshitz-Kosevich harmonic content. The effects of MI and SDS mix nonlinearly in determining the observable amplitude and phase of each resultant dHvA harmonic. One important consequence of this mixing is that the observation of a spin splitting zero of the dHvA amplitude is not indicative of equal scattering rates for spin-up and spin -down electrons, in the presence of MI. These techniques are then illustrated by applying them to studies of the dilute alloy systems Au(Fe) and au (Co), both of which are found to exhibit local magnetic moments, though apparently of quite different origin. For Au(Fe) the exchange energy shift (exchange field) and the spin-dependent scattering rates were determined as functions of (H, T). A 3:1 anisotropy of spin-up and spin-down electron scattering rates was observed for the 111 neck orbit. For Au (Co) we report the first dHvA observations of interaction effects between impurities, via measurements of the spin-dependent scattering of conduction electrons by magnetic pairs of Co impurities. We conclude that the dHvA effect appears to be a sensitive probe for determining impurity spin behavior in a magnetic field, and for measuring cyclotron orbitally averaged values of the exchange constant J _orbit, in very dilute local moment systems. Similarly, the ability to resolve spin-dependent information allows the onset of solute interactions leading to magnetism to be observed at very low solute concentrations.Research supported by NSF research grant no. DMR-07652 AO2.Guest Professor of Physics, Physics Laboratory and Research Institute for Materials, University of Nijmegen, Nijmegen, The Netherlands.     

Active coherent control of nanoscale light confinement: Modulation of plasmonic modes and position of hotspots for surface-enhanced Raman scattering detection

Multistep plasmonic nanostructures can induce the deep modulation of electromagnetic-field interactions on the nanoscale for positioning hotspots, and this generation of enhanced fields is important in many optical applications. In this article, a new strategy is proposed for fabricating a plasmonic doublestacked nanocone (DSC) nanostructure. In the DSC structure, a tunable plasmonic hybrid mode proceeds from the strong coupling of the plasmonic resonance of a fundamental cavity mode with a localized surface plasmon gap mode. In the nanostructure, the far-field response is deeply modulated and the hottest spots can be effectively positioned on the top surface of the DSC nanostructure. A controllable and cost-effective mask-reconfiguration technique for manufacturing the multiscale nanostructure is developed, which guarantees the generation of the introduced crucial stage on the DSC nanostructure. To evaluate the features of the plasmonic resonance, the DSC nanostructure is used as a surface-enhanced Raman scattering (SERS) substrate for detecting 4-mercaptopyridine molecules under specific excitation conditions. Its good performance, with an average measured SERS enhancement factor as high as 10⁸, demonstrates its strong plasmonic-mode hybridization and extreme field enhancement.

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Asymptotic expansions of the Biot-Savart law for a slender vortex with core variation

The Method of Matched Asymptotic Expansion of Singular Integrals (MAESI) is used to expand the Biot-Savart law in terms of different parameters. This method is first used to find, in terms of the small distance r to a line vortex, the first orders of the known expansion of the potential flow induced by this line vortex. This method is also used to easily compare two equations of motion of a slender vortex filament: the one obtained in an ad-hoc way by a cut-off line-integral technique and the other derived from the Navier-Stokes equations by Callegari and Ting. Finally, this method is used to give the inner expansion of the flow induced by a slender vortex in terms of its slenderness . This is the first inner expansion up to order one in terms of of the Biot-Savart law for a slender vortex. An application of this inner expansion is then given to find the induced velocity of a family of non-circular vortex rings with axisymmetric axial-core variation. In order to understand the time-evolution of these initial conditions to the Navier-Stokes equations, a short time scale is introduced. A quasi-hyperbolic system that describes the leading-order dynamics of the axisymmetric axial core variation on a curved slender vortex filament is finally extracted from the Navier-Stokes equations.     

A dynamic plasmonic manipulation technique assisted by phase modulation of an incident optical vortex beam

A novel phase modulation method for dynamic manipulation of surface plasmon polaritons?(SPPs) with a phase engineered optical vortex?(OV) beam illuminating on nanoslits is experimentally demonstrated. Because of the unique helical phase carried by an OV beam, dynamic control of SPP multiple focusing and standing wave generation is realized by changing the OV beam's topological charge constituent with the help of a liquid-crystal spatial light modulator. Measurement of SPP distributions with near-field scanning optical microscopy showed an excellent agreement with numerical predictions. The proposed phase modulation technique for manipulating SPPs features has seemingly dynamic and reconfigurable advantages, with profound potential for development of SPP coupling, routing, multiplexing and high-resolution imaging devices on plasmonic chips.     

Fluid dynamics of a quantized vortex filament in a hole

The behavior of nucleated vortex loops and of remanent vortex filaments in idealized circular and slit-like orifices has been investigated by direct computation. It is found that such vortices can be stretched by the diverging flow on the exit side of the orifice. The energy needed to stretch the vortex is abstracted from the flow field and observed as dissipation. This occurs in the form of discrete phase-slip events in the case of nucleated vortex loops, and in the form of multiple-phase-slip cascades when a remanent vortex is involved.     

Shear instabilities of a vortex lattice in layered superconductors

We study possible structures of a vortex lattice in highly layered superconductors ( _c s) with the magnetic field parallel to the layers. When the magnetic field is large and the vortex lattice is dense enough, the shear modulus is exponentially small, and one can expect the vortex lattice to melt in between the layers and a vortex smectic to be formed. For low magnetic fields the vortices are far apart, and a triangular array becomes unstable with respect to the formation of several new types of vortex lattices.     

Crystal face dependent chemical effects in surface-enhanced Raman scattering at atomically defined gold facets

Among electromagnetic and chemical (CM) contributions to surface-enhanced Raman scattering (SERS), the former is becoming controllable according to the recent progress in nanofabrication of plasmonic metal structures. However, it is still difficult to control the latter effect. Here, the degree of each contribution to SERS signals is examined on well-defined single crystalline facets of gold by using optical field localization within sphere-plane type plasmonic cavities. Crystal face dependent SERS studies of aminobenzenthiol adsorbates clearly show the distinction between CM enhancements on different surfaces, suggesting that the CM-activity of "SERS-hotspots" is closely related to interfacial dipoles formed at metal-molecular junctions.     

Proposed thermodynamic method to determine the vortex mass in layered superconductors

We describe a simple method to study vortex dynamics that can determine or set an upper limit on the vortex mass. The specific heat of the vortex lattice in layered superconductors has a classical limit of 1 k_B per pancake vortex if the vortex mass is zero. If the vortex mass m_v is finite, a new Einstein branch of normal modes will appear with a crossover temperature E m_v ^–1, and the specific heat will saturate at a new classical limit of 2 k_B per pancake vortex.This work was supported in part by AFOSR under project F49620-92-C-0004 and by NSF under grant DMR 91-20361. We acknowledge helpful discussions with Shoucheng Zhang and S. R. Patel.     

DNA Molecule as a Spintronic Device

In this work, we study the spin-dependent electron transport of a segment of DNA chain. We model the system by using the Fishbone model for DNA, which is characterized by a tight binding Hamiltonian. We predict that the spin-dependent transport can be observed in short DNA molecules coupled to metal contacts by applying an external magnetic field. A detailed analysis of spin-dependent current and spin polarization as a function of the bias voltages is carried out.     

Low noise patch‐clamp current amplification by nanoparticles plasmonic–photonic coupling (analysis and modelling)

In this article, a patch‐clamp low noise current amplification based on nanoparticles plasmonic radiation is analyzed. It is well‐known, a very small current is flowing from different membrane channels and so, for extra processing the current amplification is necessary. It is notable that there are some problems in traditional electronic amplifier due to its noise and bandwidth problem. Because of the important role of the patch‐clamp current in cancer research and especially its small amplitude, it is vital to intensify it without adding any noises. In this study, the current amplification is performed firstly: from the excitement of nanoparticles by the patch‐clamp pico‐ampere current and then, the effect of nanoparticles plasmonic far‐field radiation on conductor''s carriers, which will cause the current amplification. This relates to the plasmonic‐photonic coupling and their effect on conductor carriers as the current perturbation agent. In the steady state, the current amplification can reach to 1000 times of initial level. Furthermore, we investigated the nanoparticles morphology changing effect such as size, nanoparticles inter‐distance, and nanoparticles distance from the conductor on the amplifier parameters. Finally, it should note that the original aim is to use nanoparticles plasmonic engineering and their coupling to photonics for output current manipulating.Inspec keywords: nanoparticles, plasmonics, biomembranes, low noise amplifiers, cancer, bioelectric phenomena, nanomedicine, biomedical electronicsOther keywords: output current manipulation, NP plasmonic engineering, amplifier parameters, NP morphology changing effect, steady state, current perturbation agent, conductor carrier effect, NP plasmonic far‐field radiation effect, patch‐clamp picoampere current, bandwidth problem, noise, traditional electronic amplifier, membrane channels, nanoparticle plasmonic radiation, nanoparticle plasmonic‐photonic coupling analysis, low noise patch‐clamp current amplification     

Using optical vortex to control the chirality of twisted metal nanostructures

We discovered for the first time that light can twist metal to control the chirality of metal nanostructures (hereafter, chiral metal nanoneedles). The helicity of optical vortices is transferred to the constituent elements of the irradiated material (mostly melted material), resulting in the formation of chiral metal nanoneedles. The chirality of these nanoneedles could be controlled by just changing the sign of the helicity of the optical vortex. The tip curvature of these chiral nanoneedles was measured to be <40 nm, which is less than 1/25th of the laser wavelength (1064 nm). Such chiral metal nanoneedles will enable us to selectively distinguish the chirality and optical activity of molecules and chemical composites on a nanoscale and they will provide chiral selectivity for nanoscale imaging systems (e.g., atomic force microscopes), chemical reactions on plasmonic nanostructures, and planar metamaterials.     

Vortex lattice structure of superfluid3He-A in a magnetic field

A study is made of the lattice constructed from nonsingular vortices in superfluid³He-A in a strong magnetic field. In the presence of a magnetic field the vortex texture loses axial symmetry, and the vector outside the vortex core is nearly uniform and is directed perpendicular to the rotation axis. It is shown that the vortex lattice is spontaneously distorted and its energy depends on the orientation of the unit cell relative to the direction of the uniform vector outside the core. It is also shown that the orientation of the lattice changes when the tilting angle of the magnetic field from the rotation axis is changed. The optimum orientation angle of the distorted vortex lattice is calculated as a function of the tilting angle.     

Quantized vortex ring dynamics and the vortex core radius in He II

Using a newly developed time-of-flight technique, we have determined the temperature dependence of the vortex core radius in the range 0.35 K T 0.60 K by means of precise measurements of vortex ring dynamics. One of us (W.I.G.) has extended this work to a measurement of the pressure dependence of the vortex core radius. Our results are in agreement with the earlier work of Rayfield and Reif atT=0.28 K and zero pressure ¹ and with a model of the vortex core proposed by Glaberson, Strayer, and Donnelly. ^2,3 The precision of our measurements enabled us to observe differences in the dynamics of oppositely charged vortex rings in the same electric field configurations. We were able to quantitively account for these differences in a simple way by incorporating the frictional drag associated with the ion bound on the vortex core into the equations of motion. Our results suggest that the negative ion shape is not greatly distorted by its presence on the vortex core, nor is the negative ion strongly shielded by the vortex velocity field. Some of our results have been previously reported. ^4–6 Research supported in part by the National Science Foundation.During part of the period of this research, M. Steingart held an N.D.E.A. Title IV Fellowship.Alfred P. Sloan Foundation Fellow.     

Vortex ring propagation and interactions studies

This paper experimentally investigates the vortex ring propagation and interactions with thin cylindrical and flat surfaces. Dye-based visualization technique is adopted for the interaction studies. Vortex rings are generated from a circular nozzle of 19 mm diameter with the stroke length ratios (length of the fluid slug to nozzle diameter, L_N/D_N) of 1 to 5, and ejection velocities in the range of 0.05 to 0.2 m/s. Vortex interaction studies are carried out with two different bodies; firstly, with the circular cylinders having the diameters of 0.2, 0.6, 1.5 and 2.5 mm, and secondly with a flat solid surface. Results indicate that the trails in the vortex ring start following at L_N/D_N = 4. The influence of the initial velocity is found to be insignificant on the vortex ring diameter, however, found to depend on stroke length ratio. Vortex-cylinder interaction studies indicated that vortex velocity decreases with increase in cylinder diameter after the interaction. Reconnections of vortex rings are observed in lower cylinder diameter cases. In case of vortex ring interaction with the flat surface, stretching of the vortex core is observed leading to a considerable increase in the vortex ring diameter.