Dr Alan Drew Project Abstracts
MSci Research/Investigative Project Abstracts - note Dr Drew is only available for MSci final year project supervision.
Superconductivity in metallic bilayers
Spin-polarised Cooper pairs are capable of surviving inside a ferromagnet over much longer distances then the regular (spin-singlet, anti-parallel) Cooper pair. Evidence for proximity induced spin-triplet states inside ferromagnets have been gathered through Josephson coupling experiments, measurements of the superconductors critical temperature (Tc) and by looking for signatures of an additional induced magnetism created by the spin-triplet pairs. These Cooper pairs have potential for future application in the emerging field of super-spintronics. The best candidate material for spin-triplet superconductivity is Sr2RuO4, however with a Tc of only 1 K and extreme difficulties of fabrication in thin film form, this system is not a candidate for potential device applications. Bi in its thermodynamically stable rhombohedral structure is non-superconducting, whereas Ni is ferromagnetic that does not superconduct.
It has been recently discovered that in very thin Ni/Bi bilayers, Bi can become superconducting, with a Tc of around 4K. To further study whether the superconductivity in our Ni-Bi samples is intrinsic, we have performed a number of Andreev reflection spectroscopy, which directly probes the shape of the superconducting gap. There is a clear signature of p-wave superconductivity, and very strong evidence that the superconductivity in our samples is intrinsic and related proximity, not alloying, as NiB3 is an s-wave superconductor. This project will grow Bi and Ni layers of different thicknesses, then measure the magnetic field and temperature dependence of the resistance, with the aim of correlating layer thicknesses and structures with the superconducting critical temperature.
Exciton Dynamics in Organic Photovolatics and Light Emitting Diodes
Organic electronics has emerged as a vibrant field of research and development, spanning chemistry, physics, materials science, engineering, and technology. Whilst not destined to replace silicon-based technology, organic semiconductors promise fully flexible devices for large-area displays, solid-state lighting and solar cells. These devices mentioned share a common trait: their performance critically depends on exciton dynamics, which are not particularly well understood. This project is to characterize the exciton dynamics in organic semiconductors using a new technique that we are pioneering: photo-excited muon spin spectroscopy. This technique can be thought of as a traditional pump-probe technique, where electrons in the material are excited by light, and then the dynamics of this excitation is studied with a muon.
