Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Imaging electron flow from collimating contacts in graphene   The ballistic motion of electrons in graphene encapsulated in hexagonal boron
nitride (hBN) promises exciting opportunities for electron-optics devices. A
narrow electron beam is desired, with both the mean free path and coherence
length exceeding the device size. One can form a collimating contact in
graphene by adding zigzag contacts on either side of the electron emitter that
absorb stray electrons to form a collimated electron beam [23]. Here we provide
images of electron flow from a collimating contact that directly show the width
and shape of the electron beam, obtained using a Scanning Gate Microscope (SGM)
cooled to 4.2 K. The device is a hBN-encapsulated graphene hall bar with narrow
side contacts on either side of the channel that have an electron emitter at
the end and absorbing zig-zag contacts at both side. To form an image of
electron flow, the SGM tip is raster scanned at a constant height above the
sample surface while the transmission to a receiving contact on opposite sides
of the channel is measured. By displaying the change {\Delta}T vs. tip
position, an image of ballistic flow is obtained. The angular width of the
electron beam leaving the collimating contact is found by applying a
perpendicular magnetic field B that bends electron paths into cyclotron orbits.
SGM images reveal that electron flow from a collimating contact disappears
quickly at B = 0.05T while the flow from a non-collimating contact persists up
to B = 0.19 T. Ray tracing simulations agree well with the experimental images
over a range of B and electron density n. By fitting the half-width at half-max
(HWHM) of the magnitude of electron flow in the experimental SGM images, we
find a narrow half angular width {\Delta}{\theta} = 9.2{\deg} for the electron
flow from the collimating contact, compared with a wide flow {\Delta}{\theta} =
54{\deg} from the non-collimating contact.

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The categories of this paper are: cmp-lg
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The categories of this paper are: math
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The categories of this paper are: q-bio
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: chao-dyn