Current PhD projects on offer for a start in Sept 2021 are detailed below. Further information can be found on the School of Physics and Astronomy PhD Projects web page.
Probing Extreme States on Ultra-short Time-Scales Using XFEL Radiation
X-ray free electron lasers (XFELs) produce ultra-short (100 fs) pulses of x-ray radiation that are 109 times brighter than those available at traditional synchrotron sources. This time structure makes XFELs ideal for undertaking structural studies of the extreme states of matter that can be produced on nanosecond time-scales using laser compression techniques. The world’s first hard x-ray XFEL – the LCLS in Stanford – is already operating, and the European XFEL will start operations in Hamburg in 2017. In this project you will combine XFEL radiation with laser compression methods to make structural studies of elemental metals on ultra-short time-scales, determining the structures of the high-pressure phases, the time-scales and mechanisms of the structural phase transition mechanisms, and investigating any non-equilibrium behaviour.
High Pressure Alchemy: Turning Simple Metals into Complex Non-Metals
At ambient conditions, the group I elements (Li, Na, K, Rb Cs) are regarded as “simple metals” whose single valence electrons have only a weak interaction with the atomic core. Under pressure, however, the same simple metals are found to undergo transitions to very complex forms, which calculations suggest may be semi-metallic, or even semi-conducting. In this project, you will use nano-fabrication techniques to make “designer diamond” anvils, which will be used to measure the resistivity of alkali metals to extreme pressures. Changes in resistivity will be correlated with changes in crystal structure, determined using x-ray diffraction at the synchrotron radiation sources Diamond and the ESRF.
Probing the Behaviour of Matter at Extreme Densities Using Dynamic Compression
The upper pressure limit of the diamond anvil cell is some 4 million atmospheres (4 Mbars or 400 GPa). Pressures above this can be accesses only by dynamic compression methods, where extremely intense pulsed laser beams are used to generate a compression wave that then compresses the sample. Such techniques can generate pressures above 1 TPa (10 Mbars) and perhaps to 5 TPa or more. In this project, you will use powerful laser sources – OMEGA and JANUS, and perhaps also the National Ignition Facility (NIF), the most powerful laser in the world – to compress samples to above 1 TPa, and determine their crystal structure using nanosecond x-ray diffraction. The project will involve simulations of target designs, and will be conducted in collaboration with researchers from Lawrence Livermore National Laboratory and AWE Aldermaston.
Probing f-electron Metals at Extreme P-T
The physical properties of the lanthanide (4f) and actinide (5f) elements (Ce-Lu and Th-Lr) vary dramatically as one traverses the groups from low-Z to high-Z. The properties of any one metal can be changed in a similar manner by the application of pressure, and many of these elements undergo a sequence of structural phase transitions accompanied by changes in electronic structure. We have recently made significant progress in unravelling the complex structural sequences seen in Pr and Eu under pressure at room temperature (both of which were PhD projects), and now plan to extend these studies to higher pressures and temperatures. The project will involve experiments at synchrotron sources in the UK, France and Germany, and may also involve dynamic-compression studies at laser sources in the UK and US. This project will be conducted in collaboration with AWE Aldermaston, and the project may attract additional CASE studentship support.
Malcolm I. McMahon 