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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1780-1788 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have identified an optically enhanced magnetic phase transition in the newly synthesized organic molecular charge transfer salt, (BEDT–TTF)3Ta2F11 (BEDT–TTF 3/4 bis-ethylenedithiolotetrathiafulvalene) by ESR absorption measurements in the X band microwave region. At room temperature, only a doublet state ESR absorption is observed, but below 30 K several triplet ESR absorptions appear. The orientation dependence of the ESR absorption under illumination at energies near the band gaps in the material (640 nm, T=12 to 5 K, H0〈0.34 T) indicates that there are rapid spin exchange processes with times τe〈10−8 s near 7 to 5 K along certain crystallographic directions with a temperature dependence suggesting spin-lattice relaxation times which proceed via Van Vleck "direct processes.'' This, to our knowledge, is the first case where the magnetic properties of a charge transfer salt are altered by the interaction with photons of energy equal to the band gaps in a low dimensional solid, providing a new, interesting way to investigate these materials.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 889-891 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron-LO phonon scattering time in GaAs-Al0.33Ga0.67As quantum wells is determined to be 200±50 fs using transient absorption with low excitation density, a more direct method than previous measurement techniques.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5909-5915 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct optical coupling to the plasmon modes of a two-dimensional electron gas in a stratified semiconductor system requires an overlaid grating coupler. Plasmons can be excited with wave vectors equal to integer multiples of the grating wave vector, and the periodic screening by the grating splits these into two modes, symmetric and antisymmetric with respect to the grating profile. We present calculations of the dispersions and optical coupling strengths for several orders of both modes in a typical structure, and show that the splitting and coupling strengths of the higher order modes oscillate with varying grating mark fraction. These effects are discussed in terms of the oscillating field strengths and charge density profiles.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5249-5256 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique for engineering micron and submicron scale structures from magnetic films of transition metals has been developed using a combination of electron- and ion-beam lithography enabling high-quality arrays of submicron magnetic Fe wires to be fabricated. This process can be used to fabricate novel devices from a variety of metal combinations which would not be possible by the usual liftoff metallization method. The structure and magnetic properties are reported of an epitaxial 25 nm Fe(001)/GaAs(001) film and the wire gratings which are fabricated from it. The width of the wires in the grating is 0.5 μm for all structures studied, but the separation of each wire is varied in the range 0.5 to 16 μm. An artificially induced shape anisotropy field of around 1 kG, consistent with a magnetostatic calculation, was observed for all separations studied. The field dependence of the magneto-optic Kerr effect and magnetoresistance (MR) data is consistent with a twisted magnetization configuration across the width of the sample beneath saturation for transverse applied fields. In this case, the detailed form of the field dependence of the MR is strikingly modified from that observed in the continuous film and is consistent with coherent rotation of the magnetization.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 5658-5665 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used scanning magneto-optic Kerr effect (MOKE) microscopy to investigate the magnetic relaxation of a polycrystalline hcp 125 A(ring) Co/Si(111) film with planar uniaxial anisotropy, on time scales between 10 and 2400 s and with a spatial resolution of 15 μm. In a static magnetic field slightly less than the coercive field and applied along the easy axis direction, domains develop and the magnetization reversal proceeds via displacements of 180° domain walls. Microscopic images of this metastable state allow the 180° domains to be identified by calibration of the MOKE signal with respect to that for the saturated magnetization states. The 180° reversed domains are observed to grow in the direction of the field in the form of narrow fingers, extending via short Barkhausen jumps, randomly spaced in time over the entire time-scale range investigated, with typical distances between pinning sites of the order of microns. This reversal behavior is qualitatively similar to that reported for Au/Co perpendicular anisotropy films a few monolayers thick.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1701-1705 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the first Raman-scattering studies of the behavior of the intrasubband plasmon mode of a two-dimensional electron gas which is undergoing lateral drift in an applied electric field. The data clearly show the expected Doppler shifts of the modes traveling up- and downstream, together with the expected dependence on the wave vector, but at higher drift velocities, the expected linear shift is distorted because of electron heating effects.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1322-1326 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The far-infrared optical response of a structure consisting of a perfectly conducting grating gate on a modulation-doped GaAs/AlGaAs heterojunction has been calculated using the scattering matrix technique. The grating gate allows coupling between the incident radiation and the plasmon resonance of the two-dimensional electron gas (2DEG) in such a system, but also modifies the dispersion relation for the plasmon because of screening by the image charge distribution induced on the grating gate. Using the scattering matrix technique allows this screening effect to be modeled more accurately than has hitherto been possible, and our calculations show that the induced charge is concentrated at the edges of the grating fingers. The sinusoidal profile of the oscillating charge density in the 2DEG distorts so that the maximum amplitude of the oscillation is close to these edges, and the plasmon frequency is determined by the amount of distortion of the plasmon charge density profile and the additional screening gained through the distortion. Plasmon frequencies are calculated for a wide range of lamellar grating mark/space ratios, and are found to lie between the extremes predicted for plasmons in 2DEGs close to a vacuum interface and close to a continuous metal gate.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report far infrared (FIR) studies of plasmons in spatially modulated two-dimensional electron gases (2DEGs) in AlGaAs/GaAs heterostructures using biased overlaid metal gratings, including interdigitated gratings, both as optical couplers and as spatially modulating gates. Comparison of the experimental results with the predictions of scattering matrix calculations of the FIR response of a modulated 2DEG in the presence of a perfectly conducting lamellar grating allow us to deduce the spatial variation of the number density distribution in the 2DEG as a function of grating bias. For the interdigitated grating gates, the 2DEG can be modulated at a period of twice that of the grating fingers by differentially biasing alternate fingers; 2D plasmon resonances have been observed at half-integral values of the grating wave vector G, corresponding to the electrically induced periodicity of the 2DEG modulation itself acting as an optical coupler in addition to the metal grating. The observed G/2 plasmon frequencies decrease with increasing amplitude of the 2DEG number density modulation, in quantitative agreement with those obtained from scattering matrix calculations of the optical response of a modulated 2DEG under a perfectly conducting lamellar grating; calculations of the oscillating charge density profiles show that this occurs because, as the modulation amplitude increases, the oscillation becomes localized in regions of low 2DEG number density which are also under one of the sets of grating fingers, and is therefore better screened.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2022-2029 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present calculations of surface plasmon and guided wave enhanced light absorption in the metal electrodes of planar aluminum–aluminum oxide–silver and aluminum–aluminum oxide–aluminum tunnel junctions. We consider excitation, under conditions of attenuated total reflection, of both the "fast'' and "slow'' surface plasmons of the junction, and of TE and TM guided modes supported by a dielectric film adjoining the junction. We find that 〉97% absorption may be obtained at resonance in a single electrode of a practical device, the thickness of which is only a fraction of the expected photocarrier mean free path, and show how the angular width of the absorption peak may be varied by changing the adjacent dielectric media. We also show how resonant absorption may be used in a biased planar device for the detection of radiation at normal incidence.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of infrared and millimeter waves 14 (1993), S. 1237-1249 
    ISSN: 1572-9559
    Keywords: Plasmon ; 2DEG ; Lateral Drift ; Grating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report experimental measurements and computer calculations of the plasmon resonances of two dimensional electron gases in the far-infrared which show the effects of laterally drifting the 2DEG. Coupling to radiation is achieved using an overlaid metal grating of submicron period, and its periodic screening effect splits the plasmon into upper and lower energy modes. For a symmetric grating profile the higher energy mode is non-radiative for a stationary 2DEG and a splitting is not observable, but when the 2DEG is laterally drifted under the grating, coupling to both modes can occur, and their Doppler shifts produce an observable splitting which increases with drift velocity. These Doppler shifts are not linear with drift velocity for low velocities, but approach asymptotically the expected linear shift with increasing drift velocity. Experimental results on 2DEGs at GaAs/AlGaAs heterojunctions compare well with theoretical calculations.
    Type of Medium: Electronic Resource
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