Tuning a low density semiconducting superconductor
This project is focused on tuning low density superconductivity in semiconductors with high electron mobility. Superconducting semiconductors are rare in nature, and particularly interesting since the Fermi energy can be comparable to or smaller than the typical phonon energy scale, in contrast to virtually all other superconductors, and violating a key assumption of the conventional Bardeen-Cooper-Schrieffer theory. The ratio of the Fermi temperature to the superconducting transition temperature can also be comparable to high temperature superconducting cuprates, making them a fascinating comparative system. Given their very low densities, superconducting devices such as field-effect transistors can be made using ionic liquid gating, where the Tc can be switched on and off with a voltage. The transistor geometry also generates an asymmetric confining potential, giving a significant and tunable Rashba spin-orbit coupling which changes the spin structure of the superconducting wavefunction and the electronic band structure itself. For these reasons, this material family is increasingly being used to investigate novel phenomena in field-effect devices, and other device configurations.
The paradigmatic material in this field is the SrTiO3 (STO) system, which will be the initial target of the PhD. When doped with Zr the superconducting Tc is pushed to even lower densities, and previous studies have suggested that a Bose-Einstein condensate regime may be reached by this method. In addition to superconductivity, STO has an extremely large dielectric constant at low temperatures, formally a quantum paraelectric, which allows effective impurity screening, leading to high mobility transport properties.
A second aspect of this project is utilizing the strong photoconducting response of STO at low temperatures. The carrier density can also be tuned by ultraviolet and visible photodoping. This tuning of (super)conductivity can take place in bulk crystals as well as nano-devices. This project will leverage the results of earlier studies to provide the widest range of possible tuning parameters in the system. We will combine fundamental studies with possible interesting device architectures, nanofabrication and thin film growth.
How to apply:
Please make an online application for this project at http://www.bris.ac.uk/pg-howtoapply. Please select Physics PhD on the Programme Choice page. You will be prompted to enter details of this specific project in the ‘Research Details’ section of the form.
Anticipated start date: September 2019
Candidate requirements: A first degree in physics or a related subject, normally at a level equivalent to at least UK upper second-class honours, or a relevant postgraduate master's qualification.
See international equivalent qualifications on the International Office website.
For informal enquiries about the project please contact [[Email Address Removed]].
For enquiries about the application process contact [Email Address Removed]
Funding UK/EU: UK and EU students who meet the eligibility requirements will be considered for an EPSRC DTP studentship. Funding will cover UK/EU tuition fees, maintenance at the UKRI Doctoral Stipend rate (£14,777 per annum, 2018/19 rate) and a training support fee of £1,000 per annum for a period up to 3.5 years.
Eligibility includes, but is not limited to, being a UK or EU national who was resident in the UK for 3 years prior to the start of the project.
Funding overseas: Overseas students are also welcome to apply for a limited number of School of Physics studentships. These will be fully funded studentships to outstanding overseas candidates.
Self-funded: We welcome all-year-round applications from self-funded students and students seeking their own funding from external sources.