136 research outputs found
Nonlocal transistor based on pure crossed Andreev reflection in a EuO-graphene/superconductor hybrid structure
We study the interband transport in a superconducting device composed of
graphene with EuO-induced exchange interaction. We show that pure crossed
Andreev reflection can be generated exclusively without the parasitic local
Andreev reflection and elastic cotunnelling over a wide range of bias and Fermi
levels in an EuO-graphene/superconductor/EuO-graphene device. The pure
non-local conductance exhibits rapid on/off switching and oscillatory behavior
when the Fermi levels in the normal and the superconducting leads are varied.
The oscillation reflects the quasiparticle propagation in the superconducting
lead and can be used as a tool to probe the subgap quasiparticle mode in
superconducting graphene, which is inaccessible from the current-voltage
characteristics. Our results suggest that the device can be used as a highly
tunable transistor that operates purely in the non-local and spin-polarized
transport regime.Comment: 5 pages, 4 figures; To appear in Phys. Rev.
Klein tunneling and cone transport in AA-stacked bilayer graphene
We investigate the quantum tunneling of electrons in an AA-stacked bilayer
graphene (BLG) - junction and -- junction. We show that Klein
tunneling of an electron can occur in this system. The quasiparticles are not
only chiral but are additionally described by a `cone index'. Due to the
orthogonality of states with different cone indexes, electron transport across
a potential barrier must strictly conserve the cone index and this leads to the
protected cone transport which is unique in AA-stacked BLG. Together with the
negative refraction of electrons, electrons residing in different cones can be
spatially separated according to their cone index when transmitted across an
- junction. This suggests the possibility of `cone-tronic' devices based
on AA-stacked BLG. Finally, we calculate the junction conductance of the
system.Comment: 11 pages, 7 figures; corrected typo, final submitted versio
Injection-Limited and Space-Charge-Limited Conduction in Wide Bandgap Semiconductors with Velocity Saturation Effect
Carrier conduction in wide bandgap semiconductors (WBS) often exhibits
velocity saturation at the high-electric field regime. How such effect
influences the transition between contact-limited and space-charge-limited
current in a two-terminal device remains largely unexplored thus far. Here, we
develop a generalized carrier transport model that includes contact-limited
field-induced carrier injection, space charge, carrier scattering and velocity
saturation effect. The model reveals various transitional behaviors in the
current-voltage characteristics, encompassing Fowler-Nordheim emission,
trap-free Mott-Gurney (MG) SCLC and \emph{velocity-saturated SCLC}. Using GaN,
6H-SiC and 4H-SiC WBS as examples, we show that the velocity-saturated SCLC
completely dominates the high-voltage ( V) transport for
typical sub-m GaN and SiC diodes, thus unravelling velocity-saturated SCLC
as a central transport mechanism in WBG electronics.Comment: 8 pages, 5 figure
Universal Scaling and Signatures of Nodal Structures in Electron Tunneling from Two-Dimensional Semimetals
We present the theory of out-of-plane electron thermal-field emission from 2D
semimetals. We show that the current()-field()-temperature()
characteristic is captured by a universal scaling law applicable for broad
classes of 2D semimetals, including monolayer and few-layer graphene, nodal
point semimetals, nodal line semimetals and Dirac semimetals at the verge of
topological phase transition. The low-temperature scaling takes the universal
form, with
for 2D semimetals, which is in stark contrast to the classic Fowler-Nordheim
scaling of for 3D metals. Importantly, the Fermi level dependence
of the tunneling currents depends sensitively on the nodal structure through
the electronic density of states, thus serving as a probe for detecting the
various possible nodal structures of 2D semimetals. Our findings provide a
theoretical basis for the understanding of tunneling charge transport phenomena
in solid/vacuum and solid/solid interfaces, critical for the development of
2D-material-based vacuum and solid-state electronic devices.Comment: 8 pages, 2 figure
Over-Barrier Photoelectron Emission with Rashba Spin-Orbit Coupling
We develop a theoretical model to calculate the quantum efficiency (QE) of
photoelectron emission from materials with Rashba spin-orbit coupling (RSOC)
effect. In the low temperature limit, an analytical scaling between QE and the
RSOC strength is obtained as QE , where , and are the incident photon energy,
work function and the RSOC parameter respectively. Intriguingly, the RSOC
effect substantially improves the QE for strong RSOC materials. For example,
the QE of BiSe and Bi/Si(111) increases, by 149\% and 122\%,
respectively due to the presence of strong RSOC. By fitting to the
photoelectron emission characteristics, the analytical scaling law can be
employed to extract the RSOC strength, thus offering a useful tool to
characterize the RSOC effect in materials. Importantly, when the traditional
Fowler-Dubridge model is used, the extracted results may substantially deviate
from the actual values by , thus highlighting the importance of
employing our model to analyse the photoelectron emission especially for
materials with strong RSOC. These findings provide a theoretical foundation for
the design of photoemitters using Rashba spintronic materials.Comment: 6 pages, 3 figure
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