139 research outputs found
Low Bias Negative Differential Resistance in Graphene Nanoribbon Superlattices
We theoretically investigate negative differential resistance (NDR) for
ballistic transport in semiconducting armchair graphene nanoribbon (aGNR)
superlattices (5 to 20 barriers) at low bias voltages V_SD < 500 mV. We combine
the graphene Dirac Hamiltonian with the Landauer-B\"uttiker formalism to
calculate the current I_SD through the system. We find three distinct transport
regimes in which NDR occurs: (i) a "classical" regime for wide layers, through
which the transport across band gaps is strongly suppressed, leading to
alternating regions of nearly unity and zero transmission probabilities as a
function of V_SD due to crossing of band gaps from different layers; (ii) a
quantum regime dominated by superlattice miniband conduction, with current
suppression arising from the misalignment of miniband states with increasing
V_SD; and (iii) a Wannier-Stark ladder regime with current peaks occurring at
the crossings of Wannier-Stark rungs from distinct ladders. We observe NDR at
voltage biases as low as 10 mV with a high current density, making the aGNR
superlattices attractive for device applications.Comment: 6 pages, 4 figure
Hydrogen Bonds Dictate the Coordination Geometry of Copper: Characterization of a SquareâPlanar Copper(I) Complex
6,6â˛â˛âBis(2,4,6âtrimethylanilido)terpyridine (H2TpyNMes) was prepared as a rigid, tridentate pincer ligand containing pendent anilines as hydrogen bond donor groups in the secondary coordination sphere. The coordination geometry of (H2TpyNMes)copper(I)âhalide (Cl, Br and I) complexes is dictated by the strength of the NHâhalide hydrogen bond. The CuICl and CuIICl complexes are nearly isostructural, the former presenting a highly unusual squareâplanar geometry about CuI. The geometric constraints provided by secondary interactions are reminiscent of blue copper proteins where a constrained geometry, or entatic state, allows for extremely rapid CuI/CuII electronâtransfer selfâexchange rates. Cu(H2TpyNMes)Cl shows similar fast electron transfer (â105â
mâ1âsâ1) which is the same order of magnitude as biological systems.Entatic state: Hydrogen bonds constrain the geometry of CuI and CuII complexes. A highly unusual squareâplanar geometry about CuI (see structure) is shown to be nearly isostructural to the CuII core. The minimal reorganization energy between redox states allows for extremely rapid CuI/CuII electronâtransfer selfâexchange rates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134494/1/anie201511527_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134494/2/anie201511527-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134494/3/anie201511527.pd
CP-odd Higgs boson production in association with Neutral gauge boson in High-Energy Collisions
We study the associated production of a CP-odd Higgs boson with a
neutral gauge boson ( or photon) in high-energy collisions at the
one-loop level in the framework of Two Higgs Doublet Models (THDM). We find
that in the small regime the top quark loop contribution is
enhanced leading to significant cross-sections (about a few fb), while in the
large regime the cross-section does not attain observable rates.Comment: 16 pages Latex, 4 figures, figures in agreement with erratu
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