Organic semiconductors that are pi-conjugated are emerging as an important platform for 'spintronics', which purports to harness the spin degree of freedom of a charge carrier to store, process and/or communicate information. Here, we report the study of an organic nanowire spin valve device, 50 nm in diameter, consisting of a trilayer of ferromagnetic cobalt, an organic, Alq3, and ferromagnetic nickel. The measured spin relaxation time in the organic is found to be exceptionally long-between a few milliseconds and a second-and it is relatively temperature independent up to 100 K. Our experimental observations strongly suggest that the primary spin relaxation mechanism in the organic is the Elliott-Yafet mode, in which the spin relaxes whenever a carrier scatters and its velocity changes.

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We observe unique absorption resonances in silver/silica multilayer-based epsilon-near-zero (ENZ) metamaterials that are related to radiative bulk plasmon-polariton states of thin-films originally studied by Ferrell (1958) and Berreman (1963). In the local effective medium, metamaterial description, the unique effect of the excitation of these microscopic modes is counterintuitive and captured within the complex propagation constant, not the effective dielectric permittivities. Theoretical analysis of the band structure for our metamaterials shows the existence of multiple Ferrel-Berreman branches with slow light characteristics. The demonstration that the propagation constant reveals subtle microscopic resonances can lead to the design of devices where Ferrell-Berreman modes can be exploited for practical applications ranging from plasmonic sensing to imaging and absorption enhancement. Keywords: plasmon resonance, epsilon-near-zero, metamaterials, plasmonics An important class of artificial media are the epsilon-near-zero (ENZ) metamaterials that are designed to have a vanishing dielectric permittivity | | → 0. Waves propagating within ENZ media have a divergent phase velocity that can be used to guide light with zero phase advancement through sharp bends within sub-wavelength size channels [1, 2], or to tailor the phase of radiation/luminescence within a prescribed ENZ structure [3,4]. The electric field intensity within an ENZ medium can be enhanced relative to that in free space leading to strong light absorption [5]. This enhanced absorption in ENZ media has been exploited for novel polarization control and filtering in thin films [6], as well the proposal to use ENZ absorption resonances to tune thermal blackbody radiation of a heated object to the band-gap of a photovoltaic cell [7]. An enhanced non-linear response based upon strong spatial dispersion of waves in ENZ media has been demonstrated, and proposed for all-optical switching [8,9].Here we show theoretically and experimentally that ENZ metamaterials support unique absorption resonances related to radiative bulk plasmon-polaritons of thin metal films. These radiative bright modes exhibit properties in stark contrast to conventional dark modes of thin-film media (surface plasmon polaritons). The unique absorption resonances manifested in our metamaterials were originally studied by Ferrell in 1958 for plasmon-polaritonic thinfilms in the ultraviolet [10], and by Berreman in 1963 for phonon-polaritonic thin-films in the mid-infrared spectral region [11]. Surprisingly, two research communities have developed this independently with little communication or overlap until now: we therefore address these resonances as Ferrell-Berreman (FB) modes of our metamaterials. Counterintiutively, in the metamaterial effective medium picture, these resonances are not captured in the metamaterial dielectric permittivity constants but rather in the effective propagation constant. Furthermore, we show the existence of multiple branches of such FB modes that have slow ...

Abstract.High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is "spin selective" i.e. these materials are able to discriminate between "up" and "down" spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) ~ 50% or less. Here we consider carrier transport in an archetypical one-dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements we show that this system can act as a spin filter with maximum spin polarization approaching ~ 74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin-orbit interaction in the SWCNT channel and polarizes carrier spins. Our results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA-SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet-less and contactless spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics. 2 1. Introduction.

Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as-grown on catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ~10 4 % has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range, and can be qualitatively explained within the framework of "interlayer magnetoresistance" (ILMR).[Keywords: Graphene, Chemical Vapor Deposition, Raman Spectroscopy, Interlayer Magnetoresistance, Current-Perpendicular-to-Plane Transport] 2 Artificial layered structures often exhibit strong magnetoresistance (MR) effects that are exploited in various data storage and magnetic field sensing technologies 1 . Graphite is a naturally occurring layered material in which single graphitic layers (or "graphene") are stacked on each other. Graphene, epitaxially grown on ferromagnets (such as nickel), is particularly attractive for spintronics because such systems can potentially realize perfect spin filtering 2 and giant Rashba splitting 3 . However, CPP (current-perpendicular-toplane) MR properties of such layered graphene/ferromagnet structures are still largely underexplored. Here we consider multilayer-graphene (MLG) as-grown on nickel by chemical vapor deposition (CVD) and show that these structures exhibit large and nearly temperature-independent CPP-MR of ~ 10 4 % for a small magnetic field of ~ 2 kilogauss. This MR effect is correlated with the shape of the 2D peak and also with the occurrence of the D peak in Raman spectrum of as-grown MLG. These Raman features can be controlled by varying the CVD growth parameters. Such large negative CPP-MR, which persists even at room temperature, has hitherto not been reported in any graphitic system 4-14 . Figure 1a shows the device schematic. CVD growth of MLG is performed on 2 cm × 2 cm nickel (Ni) foils, which act as catalyst for graphene growth as well as bottom electrical contact. To ensure uniform current distribution 6 , the second contact is fabricated at the center of the top MLG surface using silver epoxy. Area of the top contact is ~ 1 mm 2 . As shown in Figure S1 (section I, Supplementary Information), the Ni substrate is polycrystalline with primarily (111) grains. Details of the fabrication process are provided in section I of Supplementary Information. Figure 1b shows a FESEM image of the as-grown large-area MLG on Ni. Raman spectra taken from three representative regions of this sample are shown in the top inset of Figure 1b. The top Raman spectrum (black line) is most commonly observed, with few occurren...