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.

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.

Preschool or prep school? Rethinking the role of early years education

Governments around the world continue to grapple with issues relating to how preschool services should be delivered, what type of provision is most appropriate, and for what purpose. These issues are particularly pertinent in a fast evolving early years sector such as the United Kingdom and many parts of the world where early years education has become a highly political topic. This article argues that given current emphasis on 'school readiness' and the formalisation of children's learning in England and internationally, tensions remain about the role of early years education and what it entails - as a nexus for enriching children's lives and learning experiences, or simply preparing children for schooling. Building on Genishi's work on rethinking dominant values of early years education and respecting the importance of inclusion and diversity, the discussion explores debates around assessment, pedagogy and the curriculum in supporting children's learning and how these are deeply embedded in wider societal values. The article calls for a rethinking of the role of early years education - the values, choices, and judgements that societies make which inform children's learning and the contexts in which they learn