Browsing by Author "Natelson, D."

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    Excess noise in STM-style break junctions at room temperature
    (American Physical Society, 2012) Chen, Ruoyu; Wheeler, Patrick J.; Natelson, D.
    Current noise in nanoscale systems provides additional information beyond the electronic conductance. We report measurements at room temperature of the nonequilibrium ﾓexcessﾔ noise in ensembles of atomic-scale gold junctions repeatedly formed and broken between a tip and a film, as a function of bias conditions. We observe suppression of the noise near conductances associated with conductance quantization in such junctions, as expected from the finite temperature theory of shot noise in the limit of few quantum channels. In higher conductance junctions, the Fano factor of the noise approaches 1/3 the value seen in the low conductance tunneling limit, consistent with theoretical expectations for the approach to the diffusive regime. At conductance values where the shot noise is comparatively suppressed, there is a residual contribution to the noise that scales quadratically with the applied bias, likely due to a flicker noise/conductance fluctuation mechanism.
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    Noise in electromigrated nanojunctions
    (American Physical Society, 2013) Wheeler, P.J.; Chen, Ruoyu; Natelson, D.
    Noise measurements are a probe beyond simple electronic transport that can reveal additional information about electronic correlations and inelastic processes. Here we report noise measurements in individual electromigrated nanojunctions, examining the evolution from the many-channel regime to the tunneling regime, using a radio frequency technique. While we generally observe the dependence of noise on bias expected for shot noise, in approximately 12% of junction configurations we find discrete changes in the bias dependence at threshold values of the bias, consistent with electronic excitation of local vibrational modes. Moreover, with some regularity we find significant mesoscopic variation in the magnitude of the noise in particular junctions even with small changes in the accompanying conductance. In another ∼17% of junctions we observe pronounced asymmetries in the inferred noise magnitude as a function of bias polarity, suggesting that investigators should be concerned about current-driven ionic motion in the electrodes even at biases well below those used for deliberate electromigration.
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    Statistical distribution of the electric field-driven switching of the Verwey state in Fe3O4
    (IOP Publishing, 2012) Fursina, A.A.; Sofin, R.G.S.; Shvets, I.V.; Natelson, D.
    The insulating state of magnetite (Fe3O4) can be disrupted by a sufficiently large dc electric field. Pulsed measurements are used to examine the kinetics of this transition. Histograms of the switching voltage show a transition width that broadens as the temperature is decreased, consistent with trends seen in other systems involving “unpinning” in the presence of disorder. The switching distributions are also modified by an external magnetic field on a scale comparable to that required to reorient the magnetization.
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    Very large magnetoresistance in Fe0.28TaS2 single crystals
    (American Physical Society, 2015) Hardy, Will J.; Chen, Chih-Wei; Marcinkova, A.; Ji, Heng; Sinova, Jairo; Natelson, D.; Morosan, E.
    Magnetic moments intercalated into layered transition metal dichalcogenides are an excellent system for investigating the rich physics associated with magnetic ordering in a strongly anisotropic, strong spin-orbit coupling environment. We examine electronic transport and magnetization in Fe0.28TaS2, a highly anisotropic ferromagnet with a Curie temperature TC∼68.8 K. We find anomalous Hall data confirming a dominance of spin-orbit coupling in the magnetotransport properties of this material, and a remarkably large field-perpendicular-to-plane magnetoresistance (MR) exceeding 60% at 2 K, much larger than the typical MR for bulk metals, and comparable to state-of-the-art giant MR in thin film heterostructures, and smaller only than colossal MR in Mn perovskites or high mobility semiconductors. Even within the FexTaS2 series, for the current x=0.28 single crystals the MR is nearly 100× higher than that found previously in the commensurate compound Fe0.25TaS2. After considering alternatives, we argue that the large MR arises from spin-disorder scattering in the strong spin-orbit coupling environment, and suggest that this can be a design principle for materials with large MR.