54 research outputs found
Imaging and controlling electron transport inside a quantum ring
Traditionally, the understanding of quantum transport, coherent and
ballistic1, relies on the measurement of macroscopic properties such as the
conductance. While powerful when coupled to statistical theories, this approach
cannot provide a detailed image of "how electrons behave down there". Ideally,
understanding transport at the nanoscale would require tracking each electron
inside the nano-device. Significant progress towards this goal was obtained by
combining Scanning Probe Microscopy (SPM) with transport measurements2-7. Some
studies even showed signatures of quantum transport in the surrounding of
nanostructures4-6. Here, SPM is used to probe electron propagation inside an
open quantum ring exhibiting the archetype of electron wave interference
phenomena: the Aharonov-Bohm effect8. Conductance maps recorded while scanning
the biased tip of a cryogenic atomic force microscope above the quantum ring
show that the propagation of electrons, both coherent and ballistic, can be
investigated in situ, and even be controlled by tuning the tip potential.Comment: 11 text pages + 3 figure
Imaging Electron Wave Functions Inside Open Quantum Rings
Combining Scanning Gate Microscopy (SGM) experiments and simulations, we
demonstrate low temperature imaging of electron probability density
in embedded mesoscopic quantum rings (QRs). The tip-induced
conductance modulations share the same temperature dependence as the
Aharonov-Bohm effect, indicating that they originate from electron wavefunction
interferences. Simulations of both and SGM conductance maps
reproduce the main experimental observations and link fringes in SGM images to
.Comment: new titl
Local Density of States in Mesoscopic Samples from Scanning Gate Microscopy
We study the relationship between the local density of states (LDOS) and the
conductance variation in scanning-gate-microscopy experiments on
mesoscopic structures as a charged tip scans above the sample surface. We
present an analytical model showing that in the linear-response regime the
conductance shift is proportional to the Hilbert transform of the
LDOS and hence a generalized Kramers-Kronig relation holds between LDOS and
. We analyze the physical conditions for the validity of this
relationship both for one-dimensional and two-dimensional systems when several
channels contribute to the transport. We focus on realistic Aharonov-Bohm rings
including a random distribution of impurities and analyze the LDOS-
correspondence by means of exact numerical simulations, when localized states
or semi-classical orbits characterize the wavefunction of the system.Comment: 8 pages, 8 figure
Unraveling quantum Hall breakdown in bilayer graphene with scanning gate microscopy
We use low-temperature scanning gate microscopy (SGM) to investigate the
breakdown of the quantum Hall regime in an exfoliated bilayer graphene flake.
SGM images captured during breakdown exhibit intricate patterns of "hotspots"
where the conductance is strongly affected by the presence of the tip. Our
results are well described by a model based on quantum percolation which
relates the points of high responsivity to tip-induced scattering between
localized Landau levels.Comment: 6 pages, 4 figure
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