21 research outputs found
Methods for environment: productivity trade-off analysis in agricultural systems
Trade-off analysis has become an increasingly important approach for evaluating system level outcomes of agricultural production and for prioritising and targeting management interventions in multi-functional agricultural landscapes. We review the strengths and weakness of different techniques available for performing trade-off analysis. These techniques, including mathematical programming and participatory approaches, have developed substantially in recent years aided by mathematical
advancement, increased computing power, and emerging insights into systems behaviour. The strengths and weaknesses of the different approaches are identified and discussed, and we make suggestions for a tiered approach for situations with different data availability. This chapter is a modified and extended version of Klapwijk et al. (2014)
Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions
The rise of topological phases of matter is strongly connected to their
potential to host Majorana bound states, a powerful ingredient in the search
for a robust, topologically protected, quantum information processing. In order
to produce such states, a method of choice is to induce superconductivity in
topological insulators. The engineering of the interplay between
superconductivity and the electronic properties of a topological insulator is a
challenging task and it is consequently very important to understand the
physics of simple superconducting devices such as Josephson junctions, in which
new topological properties are expected to emerge. In this article, we review
recent experiments investigating topological superconductivity in topological
insulators, using microwave excitation and detection techniques. More
precisely, we have fabricated and studied topological Josephson junctions made
of HgTe weak links in contact with two Al or Nb contacts. In such devices, we
have observed two signatures of the fractional Josephson effect, which is
expected to emerge from topologically-protected gapless Andreev bound states.
We first recall the theoretical background on topological Josephson junctions,
then move to the experimental observations. Then, we assess the topological
origin of the observed features and conclude with an outlook towards more
advanced microwave spectroscopy experiments, currently under development.Comment: Lectures given at the San Sebastian Topological Matter School 2017,
published in "Topological Matter. Springer Series in Solid-State Sciences,
vol 190. Springer
Ge/Si nanowire mesoscopic Josephson junctions
The controlled growth of nanowires (NWs) with dimensions comparable to the
Fermi wavelengths of the charge carriers allows fundamental investigations of
quantum confinement phenomena. Here, we present studies of proximity-induced
superconductivity in undoped Ge/Si core/shell NW heterostructures contacted by
superconducting leads. By using a top gate electrode to modulate the carrier
density in the NW, the critical supercurrent can be tuned from zero to greater
than 100 nA. Furthermore, discrete sub-bands form in the NW due to confinement
in the radial direction, which results in stepwise increases in the critical
current as a function of gate voltage. Transport measurements on these
superconductor-NW-superconductor devices reveal high-order (n = 25) resonant
multiple Andreev reflections, indicating that the NW channel is smooth and the
charge transport is highly coherent. The ability to create and control coherent
superconducting ordered states in semiconductor-superconductor hybrid
nanostructures allows for new opportunities in the study of fundamental
low-dimensional superconductivity