5,382 research outputs found
Transition from ultrafast laser photo-electron emission to space charge limited current in a 1D gap
A one-dimensional (1D) model has been constructed to study the transition of
the time-dependent ultrafast laser photo-electron emission from a flat metallic
surface to the space charge limited (SCL) current, including the effect of
non-equilibrium laser heating on metals at the ultrafast time scale. At a high
laser field, it is found that the space charge effect cannot be ignored and the
SCL current emission is reached at a lower value predicted by a short pulse SCL
current model that assumed a time-independent emission process. The threshold
of the laser field to reach the SCL regime is determined over a wide range of
operating parameters. The calculated results agree well with particle-in-cell
(PIC) simulation. It is found that the space charge effect is more important
for materials with lower work function like tungsten (4.4 eV) as compared to
gold (5.4 eV). However for a flat surface, both materials will reach the space
charge limited regime at the sufficiently high laser field such as 5 GV/m
with a laser pulse length of tens to one hundred femtoseconds.Comment: 12 pages, 3 figures, printed in {\itshape J. Phys. D: Appl. Phys.
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.
- …