52 research outputs found
Electronic transport in a two-dimensional superlattice engineered via self-assembled nanostructures
Nanoscience offers a unique opportunity to design modern materials from the
bottom up, via low-cost, solution processed assembly of nanoscale building
blocks. These systems promise electronic band structure engineering using not
only the nanoscale structural modulation, but also the mesoscale spatial
patterning, although experimental realization of the latter has been
challenging. Here we design and fabricate a new type of artificial solid by
stacking graphene on a self-assembled, nearly periodic array of nanospheres,
and experimentally observe superlattice miniband effects. We find conductance
dips at commensurate fillings of charge carriers per superlattice unit cell,
which are key features of minibands that are induced by the quasi-periodic
deformation of the graphene lattice. These dips become stronger when the
lattice strain is larger. Using a tight-binding model, we simulate the effect
of lattice deformation as a parameter affecting the inter-atomic hopping
integral, and confirm the superlattice transport behavior. This 2D
material-nanoparticle heterostructure enables facile band structure engineering
via self-assembly, promising for large area electronics and optoelectronics
applications
Fate of global superconductivity in arrays of long SNS junctions
Normal-metal films overlaid with arrays of superconducting islands undergo
Berezinskii-Kosterlitz-Thouless (BKT) superconducting transitions at a
temperature . We present measurements of T for arrays of
mesoscopic Nb islands patterned on Au films for a range of island spacings .
We show that , and explain this dependence in terms of the
quasiclassical prediction that the Thouless energy, rather than the
superconducting gap, governs the inter-island coupling. We also find two
deviations from the quasiclassical theory: (i) is sensitive to island
height, because the islands are mesoscopic; and (ii) for widely spaced islands
the transition appears to lead, not to a superconducting state, but to a
finite-resistance "metallic" one.Comment: 12 pages, 4 figure
Single Gate P-N Junctions in Graphene-Ferroelectric Devices
Graphene's linear dispersion relation and the attendant implications for
bipolar electronics applications have motivated a range of experimental efforts
aimed at producing p-n junctions in graphene. Here we report electrical
transport measurements of graphene p-n junctions formed via simple
modifications to a PbZrTiO substrate, combined with a
self-assembled layer of ambient environmental dopants. We show that the
substrate configuration controls the local doping region, and that the p-n
junction behavior can be controlled with a single gate. Finally, we show that
the ferroelectric substrate induces a hysteresis in the environmental doping
which can be utilized to activate and deactivate the doping, yielding an
`on-demand' p-n junction in graphene controlled by a single, universal
backgate
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