Lecturer: Dr. Moshe Ben Shalom
Affiliation: School of Physics & Astronomy
The University of Manchester
Abstract:
Research in graphene has evolved into a stage
in which other isolated atomic planes of
materials can now be reassembled in a chosen
sequence, as in building with Lego where the
blocks are defined with one-atomic-plane
precision [1]. Due to their weak interlayer
forces “Van der Waals” crystals can be
separated to individual layers of a single
crystallographic domain before reorienting and
transferring them to form a new stack. The first
part of the talk is aimed to give a wide review of
the recent research done in Manchester in this
field, with emphasize on ways to study
materials which are unstable in ambient
conditions [2].
The second part will focus on hetrostructures in
which graphene is stacked between hexagonal
boron nitride crystals (hBN), where electrons
can travel for many micrometres before
experiencing any scattering or de-coherence; I
will first describe the extremely high
superconducting currents which can be driven
along graphene by placing it in proximity to a
superconductor [3]. Remarkably, these currents
persist even in the presence of high magnetic
fields such that graphene can, in principle, be
tuned into the Quantum Hall regime. The
proximity-induced supercurrent, however, is
found to be mediated by mesoscopic
trajectories at the edges and its cut-off is prior
to the onset of the QH. Next, I will discuss the
nature of current flow when breaking the
inversion symmetry of the system and opening
an energy gap. Topological valley currents are
predicted when placing the chemical potential
in the gap. Lastly, I will present experimental
observations of hydrodynamic-like flow and
formation of electron-whirlpools in this system
at higher temperatures [4].
[1] "Van der Waals heterostructures."
Nature499.7459 (2013): 419-425.
[2] “Quality heterostructures from two
dimensional crystals unstable in air by their
assembly in inert atmosphere” Nano letters
15(8),4914 (2015)
[3] "Proximity superconductivity in ballistic
graphene, from Fabry-Perot oscillations to
random Andreev states in magnetic field."
arXiv:1504.03286.
[4] "Negative local resistance due to viscous
electron backflow in graphene."
arXiv:1509.04165.