Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

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Surface plasmon subwavelength optics

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

We present experimental scattering data at microwave frequencies on a structured metamaterial that exhibits a frequency band where the effective index of refraction (n) is negative. The material consists of a two-dimensional array of repeated unit cells of copper strips and split ring resonators on interlocking strips of standard circuit board material. By measuring the scattering angle of the transmitted beam through a prism fabricated from this material, we determine the effective n, appropriate to Snell's law. These experiments directly confirm the predictions of Maxwell's equations that n is given by the negative square root of epsilon.mu for the frequencies where both the permittivity (epsilon) and the permeability (mu) are negative. Configurations of geometrical optical designs are now possible that could not be realized by positive index materials.

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Experimental Verification of a Negative Index of Refraction

The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for improved photovoltaic devices

Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

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Controlling Electromagnetic Fields

Modes for transmission of microwaves through alkali metals at cryogenic temperatures

Observations of discrete jumps allowing determination of the statistics for magnetization reversal of interacting magnetic particles in CoCr thin-films

A new technique is discussed which utilizes conduction-electron-spin resonance (CESR) in metal bilayers to determine the electron-spin susceptibility of metals. Transmission electron-spin resonance measurements are performed on bilayers made from various pairs of the metals lithium, sodium, potassium, copper, and silver. These measurements allow a determination of the ratio of the electron-spin susceptibilities of the two metals constituting the bilayer. Combining previously measured values of the electron-spin susceptibility of Na and K with our bilayer data, and performing a least-squares analysis, yields values of the electron-spin susceptibility of Li, Cu, and Ag. The resulting values are (2.29\ifmmode\pm\else\textpm\fi{}0.13)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cgs volume units for lithium, (1.35\ifmmode\pm\else\textpm\fi{}0.06)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cgs volume units for copper, and (0.86\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cgs volume units for silver. These values agree with theoretical estimates and other experimental determinations. The self-consistency of our results also supports the reliability of our technique. This technique is potentially applicable to all metals for which CESR can be observed, and we discuss some possible candidates for future bilayer CESR susceptibility measurements.

Measurement of the electron-spin susceptibility of Li, Cu, and Ag via transmission conduction-electron-spin resonance in metallic bilayers

Development toward magneto-optic Kerr scanned near-field optical microscope with 10 nm resolutionS. Schultz and T. J. SilvaUniversity of California, San Diego, Department of Physics 03199500 Gilman Dr., La Jolla, CA 92093-03 19ABSTRACTWork is described on the development of a £canned Near-field Qptical Microscope (SNOM) to observemagnetization distributions with sub-wavelength resolution. Contrast is provided by the magneto-opticKerr effect. A single Ag particle of -30 nm diameter was chosen as a SNOM probe for reasons unique to

Development toward magneto-optic Kerr scanned near-field optical microscope with 10 nm resolution

We report a magnetic-resonance study of Gd-doped ${\mathrm{Eu}}_{2}$${\mathrm{CuO}}_{4}$ single crystals. Cooling the samples in a magnetic field ${\mathbf{H}}_{\mathrm{FC}}$, induces weak ferromagnetism (WF), with a strong out-of-plane anisotropy determined by the Dzyaloshinsky-Moriya (DM) interaction. In addition, there is in-plane anisotropy with an easy-axis parallel to the [110] crystal axis closest to ${\mathbf{H}}_{\mathrm{FC}}$. An intense resonance mode is observed at the X band (9.5 GHz) when ${\mathbf{H}}_{\mathrm{FC}}$ is applied parallel to one of the 〈110〉 axes and the measuring field is rotated by 90\ifmmode^\circ\else\textdegree\fi{} in the ${\mathrm{CuO}}_{2}$ plane. At the Q band (35 GHz), the in-plane resonance modes strongly depend on angle and temperature. We analyze the experimental results in terms of a phenomenological model for the magnetic free energy, which predicts a reorientation transition of the WF component of the magnetization ${\mathbf{m}}_{\mathrm{WF}}$ induced by the external field. Associated with this transition, a softening of the WF magnetic resonance mode occurs when the external field is applied perpendicular to the easy magnetization axis. The resulting angular variation of the resonance modes depends on whether the energy gap for the magnetic excitations is larger or smaller than the microwave energy. From the resonance data we have determined both the out-of-plane and in-plane anisotropy fields, ${\mathit{H}}_{\mathrm{DM}}$(T) and ${\mathit{H}}_{\mathrm{ax}}$(T), respectively.The extrapolated values for T=0 are ${\mathit{H}}_{\mathrm{DM}}$(0)=3.5(5)\ifmmode\times\else\texttimes\fi{}${10}^{5}$ G and ${\mathit{H}}_{\mathrm{ax}}$(0)=12(2) G. Both anisotropy fields decrease with increasing T, vanishing around ${\mathit{T}}_{\mathit{N}}$\ensuremath{\simeq}243 K. The temperature dependence of the peak-to-peak linewidths, \ensuremath{\Delta}${\mathit{H}}_{\mathrm{pp}}$, measured at the X and Q bands is explained in terms of a temperature-independent frequency linewidth, \ensuremath{\Delta}${\mathrm{\ensuremath{\omega}}}_{1/2}$/\ensuremath{\gamma}=1.6(2) kG. Nonresonant absorption losses around the maxima and minima of the \ensuremath{\omega}/\ensuremath{\gamma} vs H curves are also described in terms of this finite width for the resonance modes.

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Sheldon Schultz

Papers

Modes for transmission of microwaves through alkali metals at cryogenic temperatures

Observations of discrete jumps allowing determination of the statistics for magnetization reversal of interacting magnetic particles in CoCr thin-films

Measurement of the electron-spin susceptibility of Li, Cu, and Ag via transmission conduction-electron-spin resonance in metallic bilayers

Development toward magneto-optic Kerr scanned near-field optical microscope with 10 nm resolution

Field-induced spin reorientation in Eu2CuO4:Gd studied by magnetic resonance.