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Grant Nunn

Publications and source records attributed to Grant Nunn.

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An epitaxial graphene platform for zero-energy edge state nanoelectronics

Graphene's original promise to succeed silicon faltered due to pervasive edge disorder in lithographically patterned deposited graphene and the lack of a new electronics paradigm. Here we demonstrate that the annealed edges in conventionally patterned graphene epitaxially grown on a silicon carbide substrate (epigraphene) are stabilized by the substrate and support a protected edge state. The edge state has a mean free path that is greater than 50 microns, 5000 times greater that the bulk states and involves a theoretically unexpected Majorana-like zero-energy non-degenerate quasiparticle that does not produce a Hall voltage. In seamless integrated structures, the edge state forms a zero-energy one-dimensional ballistic network with essentially dissipationless nodes at ribbon-ribbon junctions. Seamless device structures offer a variety of switching possibilities including quantum coherent devices at low temperatures. This makes epigraphene a technologically viable graphene nanoelectronics platform that has the potential to succeed silicon nanoelectronics.

cond-mat.mes-hall

Probing the Magnetodynamics of Magnetic Tunnel Junctions with the Aid of SiGe HBTs

High impedance (about 1 Megaohm) magnetic tunnel junctions (MTJs) are used to observe and record the magnetodynamics of the nanomagnets that form the junctions themselves. To counteract the bandwidth limitations caused by the high impedance of the junction and the parasitic capacitance intrinsic to any cryogenic system, silicon-germanium heterojunction bipolar transistors (SiGe HBTs) are used as cryogenic preamplifiers for the MTJs. The resulting measurement improvements include an increase in bandwidth by a factor of 3.89, an increase in signal-to-noise ratio by a factor of 6.62, and a gain of 7.75 of the TMR signal produced by the MTJ. The limitation to the measurement system was found to be from the external, room temperature electronics. Despite this limitation, these improvements allow for better time-resolved magnetodynamics measurements of the MTJs. These experiments pave the way for future cryogenic, magnetodynamics measurement improvements, and could even be useful in cryogenic memory applications.

cond-mat.mes-hall