PhD projects
Projects available for DPhil projects from October 2026 in our group are listed below. Please get in touch with Professor 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, in particular understanding superconductivity and the competing electronic phases. Suitable candidates need to have a good understanding of condensed matter physics and good computing skills (Python, Matlab) as well the ability to work well in an experimental team. Most of our projects have both experimental and computational components which can include first-principle calculations.
Funding
Our projects on superconductivity are proposed for funding via the Superconductivity CDT and students are advised to apply via the official Superconductivity website in Oxford. Due to the high competition for funded places candidates are advised to consider and apply for relevant funding. Details about the DPhil application process via the Condensed Matter Physics application can be found here and to the available scholarships in Oxford can be found here.
1. Strain-tuning of Superconducting and Competing Electronic Phases in Iron-Chalcogenide Superconductors
Uniaxial pressure is a powerful tuning parameter of correlated electronic phases of matter and relevant in superconducting applications. This technique can enhance superconductivity, it provides a unique insight into the behaviour of nematic electronic states giving access to the anisotropic Fermi surfaces, via the nematic susceptibility, and it can break the translational symmetry to stabilize novel topological phases of matter [1,2]. This project will use applied strain to tune the superconducting and the electronic structure. This will help develop a strategy about how to enhance superconductivity, and identify whether the pairing interaction is related to the nematic or magnetic fluctuations [3]. Additionally, elastocaloric effect can be used to probe second-order phase transitions to study the nature of complex pairing symmetries in iron-based superconductors [4].
Firstly, the student will perform transport and magnetotransport measurements under strain in high magnetic fields and it will establish how the superconducting phase diagrams are affected by applied strain. These studies will be extended in magnetic fields up to 90T to assess the changes in the Fermi surface under applied strain. Additionally, the student will develop capabilities to measure elastocaloric effect to determine the changes in temperature to an oscillating uniaxial stress at the superconducting phase transitions. The strain will be applied using both piezostacks and Razorbill cells to tune electronic nematic phases and to assess the strain dependence of critical temperature. The student will use finite element analysis software to simulate the expected strain transmission for the different experimental strain design and cells. The student will be able to perform first-principle calculations to simulate the changes in the electronic structure under strain.
Experiments in high magnetic fields will be performed at international high-magnetic field facilities in Europe and USA. As applied strain is relevant for technological applications, during the project the student could also test the strain variation of the critical currents of wires and tapes used in superconducting applications.
This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics.
For further reading please consult:
1. Emergence of the nematic electronic state in FeSe
https://doi.org/10.1103/PhysRevB.91.155106
2. Strain tuning of nematicity and superconductivity in single crystals of FeSe
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.205139
3. Iron pnictides and chalcogenides: a new paradigm for superconductivity
https://www.nature.com/articles/s41586-021-04073-2
https://arxiv.org/abs/2201.02095
4. AC elastocaloric effect as a probe for thermodynamic signatures of continuous phase transitions https://doi.org/10.1063/1.5099924
2. High-Magnetic Fields to explore Phase Diagrams of Novel Superconductors
In order to understand the relevance of novel superconductors for practical application one needs to understand in detail the three-dimensional phase diagram of superconductors using temperatures, magnetic field and critical fields. These phase diagrams can be constructed using a variety of experimental techniques which include resistivity measurements to test the zero-resistance state and the critical currents, torque measurements which probe the irreversibility fields and tunnel diode oscillator studies which can access the penetration depth. Magnetization measurements can be used to detect the upper and lower critical fields, the pinning forces as well as to estimate the critical currents using the Bean model and correcting for the demagnetizing effects.
This project will construct in detail the superconducting phase diagrams of novel crystalline superconducting materials, which would include iron-based superconductors and candidate topological superconductors. Experiments will be performed as a function of temperature and magnetic fields both in Oxford using high-magnetic fields up to 21T and at the high-magnetic field facilities in Europe and USA. The upper critical fields will be modelled using both single band and multi-band models as applied to other iron-based superconductors. The superconducting fluctuations will be explored using torque magnetometry and paraconductivity studies.
This project can be extended to explore superconducting wires and tapes relevant for practical applications using a designed probes for critical current studies up to 500 A in 14T at 4.2K.
This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics. This project will be co-supervised by Professor Amalia Coldea and Professor Stephen J. Blundell.
For further reading please consult relevant papers:
1. Ultra-high critical current densities, the vortex phase diagram and the effect of granularity of the stoichiometric high-Tc superconductor, CaKFe4As4
https://arxiv.org/abs/1808.06072
2. Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor, CaKFe4As4
https://arxiv.org/abs/2003.02888
3. Multi-band description of the upper critical field of bulk FeSe
https://arxiv.org/abs/2311.04188
3. Developing tunable superconducting devices based on thin flakes of iron-chalcogenide superconductors
Iron-chalcogenide superconductors are versatile materials composed of conducting two-dimensional iron planes separated by van der Waals layers of chalcogens. When FeSe is grown as a monolayer on a suitable substrate, it exhibits the highest critical transition temperature among two-dimensional systems, exceeding that of liquid nitrogen [1]. Furthermore, ionic-liquid gating of FeSe films induces electron doping, enhancing superconductivity four-fold to around 45 K [2]. Thin flakes of FeSe also demonstrate a superconducting diode effect, where zero-resistance states appear non-reciprocally during current injection [3].
This project aims to explore the superconducting and electronic behaviour of dimensional devices based on thin flakes of highly crystalline iron chalcogenides (FeSe1-xSx and FeSe1-xTex). Different ionic substrates and electrochemical gating will be used to tune carrier concentrations and enhance superconductivity. These studies will help establish the link between superconducting phases, electron doping, and competing nematic and magnetic phases, as well as identify signatures of topological behaviour and the superconducting diode effect. The student will investigate phase diagrams and normal electronic manifestations in novel superconducting thin flake devices, tuned via flake thickness and electrochemical gating. The project will involve device preparation, critical current measurements, magnetotransport, and Hall effect studies to explore electronic properties and superconducting phase diagrams under high magnetic fields and low temperatures. Experiments will search for quantum oscillations in the best candidate systems with large mean free paths, utilizing high magnetic field facilities in Europe and the USA. The thin flakes will be exfoliated from existing single crystals using previously developed methods [4,5]. Sample preparation will include designing appropriate lithographic patterns via optical and e-beam lithography, mechanical exfoliation, and using a glove box to handle air-sensitive samples. This project could also be extended to include simulations of current distributions in devices using finite element analysis, to better quantify and understand current distribution.
This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics.
For further reading please consult:
1. Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3
https://doi.org/10.1038/nmat4153
2. Interplay between superconductivity and the strange-metal state in FeSe
https://doi.org/10.1038/s41567-022-01894-4
3. Field-free superconducting diode effect in layered superconductor FeSe
https://arxiv.org/abs/2409.01715
4. Suppression of superconductivity and enhanced critical field anisotropy in ultra-thin flakes of FeSe
https://www.nature.com/articles/s41535-020-0227-3
5. Unconventional localization of electrons inside of a nematic electronic phase,
https://www.pnas.org/doi/10.1073/pnas.2200405119