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Borunda, Mario

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Borunda

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Mario

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Borunda, Mario

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2010 - 20163

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Author's Publications: search.filters.isAuthorOfPublication.64d7eb6e-35c8-4cb1-ba2b-1708ecb8adad

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    Theory of Graphene Raman Scattering
    (American Chemical Society (ACS), 2016) Heller, Eric; Yang, Yuan; Kocia, Lucas; Chen, Wei; Fang, Shiang; Borunda, Mario; Kaxiras, Efthimios
    Raman scattering plays a key role in unraveling the quantum dynamics of graphene, perhaps the most promising material of recent times. It is crucial to correctly interpret the meaning of the spectra. It is therefore very surprising that the widely accepted understanding of Raman scattering, i.e., Kramers–Heisenberg–Dirac theory, has never been applied to graphene. Doing so here, a remarkable mechanism we term“transition sliding” is uncovered, explaining the uncommon brightness of overtones in graphene. Graphene’s dispersive and fixed Raman bands, missing bands, defect density and laser frequency dependence of band intensities, widths of overtone bands, Stokes, anti-Stokes anomalies, and other known properties emerge simply and directly.
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    Imaging Universal Conductance Fluctuations in Graphene
    (American Chemical Society (ACS), 2011) Borunda, Mario; Berezovsky, Jesse; Westervelt, Robert; Heller, Eric
    We study conductance fluctuations (CF) and the sensitivity of the conductance to the motion of a single scatterer in two-dimensional massless Dirac systems. Our extensive numerical study finds limits to the predicted universal value of CF. We find that CF are suppressed for ballistic systems near the Dirac point and approach the universal value at sufficiently strong disorder. The conductance of massless Dirac fermions is sensitive to the motion of a single scatterer. CF of order e2/h result from the motion of a single impurity by a distance comparable to the Fermi wavelength. This result applies to graphene systems with a broad range of impurity strength and concentration while the dependence on the Fermi wavelength can be explored via gate voltages. Our prediction can be tested by comparing graphene samples with varying amounts of disorder and can be used to understand interference effects in mesoscopic graphene devices.
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    Imaging Coherent Transport in Graphene (Part I): Mapping Universal Conductance Fluctuations
    (Institute of Physics, 2010) Berezovsky, Jesse; Borunda, Mario; Heller, Eric; Westervelt, Robert
    Graphene provides a fascinating testbed for new physics and exciting opportunities for future applications based on quantum phenomena. To understand the coherent flow of electrons through a graphene device, we employ a nanoscale probe that can access the relevant length scales—the tip of a liquid-He-cooled scanning probe microscope (SPM) capacitively couples to the graphene device below, creating a movable scatterer for electron waves. At sufficiently low temperatures and small size scales, the diffusive transport of electrons through graphene becomes coherent, leading to universal conductance fluctuations (UCF). By scanning the tip over a device, we map these conductance fluctuations versus scatterer position. We find that the conductance is highly sensitive to the tip position, producing \(\delta G \sim e^2/h\) fluctuations when the tip is displaced by a distance comparable to half the Fermi wavelength. These measurements are in good agreement with detailed quantum simulations of the imaging experiment and demonstrate the value of a cooled SPM for probing coherent transport in graphene.