PhD projects 2021

Projects available in our group for 2021 are listed below. Please get in touch with Dr Amalia Coldea (amalia.coldea@physics.ox.ac.uk) for further details.
We welcome applications from enthusiastic students who are excited and challenged by understanding the rich novel physical phenomena displayed by novel quantum materials.

1.Ultra-high magnetic fields for understanding complex quantum materials

Magnetic fields are a unique tool to explore and tune quantum materials towards extreme experimental regimes in which new phases of matter can be stabilized. Additionally, magnetic fields are essential to characterize the phase diagram of novel superconductors to identify suitable candidates for practical applications. This is an experimental project to explore and develop new experimental techniques for studying quantum materials in ultra-high magnetic fields. The quantum materials to be explored will include novel iron-based superconductors and molecular magnets, as well as systems in which the spin, electronic and lattice degrees of freedom interact strongly and can be disturbed by a magnetic field.

The student will be combining transport and thermodynamic techniques using superconducting magnets and pulsed field magnets available in Oxford. The pulsed magnetic fields are short in duration but up to a factor of 3 times higher than the field produced by superconducting magnets. Oxford has a long tradition in high magnetic field research having the largest magnetic fields in the UK for condensed matter physics both using pulsed field in the Nicholas Kurti High Magnetic Field Laboratory as well as superconducting magnets up to 21T as part of the High Magnetic Field facilities and the new Oxford Centre for Applied Superconductivity (http://www.cfas.ox.ac.uk/).

A suitable candidate needs to have a good understanding of condensed matter physics and good computational skills as well the ability to work well in an experimental team. The student will be co-supervised by Professor Stephen Blundell and Professor Amalia Coldea.

2. Developing electronic tunable devices of thin flakes of iron-based superconductors

This project is to explore electronic and topological behaviour of quasi-two dimensional devices based on thin flakes of highly crystalline superconducting iron-based chalcogenides as well as Dirac and Weyl semimetals. The project will involve device preparation and a suite of physical properties measurements to study their electronic properties using high magnetic field and low temperatures. The aim is to search for quantum phenomena as well as for signature of topological matter in these highly tunable quantum material devices. The project will be hosted by the recently funded Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics. The student will investigate the phase diagrams of novel superconducting thin flake devices under different extreme conditions of high magnetic field, strain and pressure. Experiments using advanced techniques for transport will be performed using high magnetic field facilities available in Oxford and elsewhere. A suitable candidate needs to have a good understanding of condensed matter physics and good computing skills as well the ability to work well in an experimental team.

3. Tuning electronic ground states and superconductivity of iron-based superconductors under extreme experimental conditions

Applied hydrostatic pressure is a unique tuning parameter to study the characteristics of a nematic quantum critical point in the absence of long-range magnetic order in a single material and to gives access to the electronic structure and correlations of new magnetic and structural phases. FeSe is an unique superconductor that show a nematic electronic phase in which absence of magnetism at ambient pressure. However, a magnetic phase is stabilized at high pressure and superconductivity is enhanced four-fold. By combining the chemical pressure with the hydrostatic pressure in the series FeSe1-xSx, it is possible to separate the nematic and magnetic phases. This project will aim to understand the evolution of the complex Fermi surfaces and electronic interactions across the nematic phase transitions using applied hydrostatic pressure in different iron-based superconductors. High magnetic field and low temperatures will be used to access directly the Fermi surface by detecting quantum oscillations in different ground states tuned by applied hydrostatic pressure. A suitable candidate needs to have a good understanding of condensed matter physics and good experimental and computational skills as well the ability to work well in an experimental team.

4. Revealing topological signatures in the electronic behaviour of bulk quantum materials with Dirac dispersion

This is an experimental project combining electronic transport and quantum oscillations to detect unusual signatures of the manifestation of topology in single crystals of quantum materials with Dirac dispersions. The student will perform a series of studies in high magnetic fields and at low temperatures to search for evidence of non-trivial Berry phases and low temperature quantum transport. Studies will be also extended under applied pressure and strain to identify proximity to new toplogical superconducting phase. The work will be combined with first-principle band structure calculations to compare with experiments and disentangle trivial from non-trivial effects. A suitable candidate needs to have a good understanding of condensed matter physics and good computing skills as well the ability to work well in an experimental team.

Details about the application process can be found here and concerning the available scholarships can be found here.