High-temperature Superconductivity in Hydride Compounds
A position is available to study record superconductors as part of a 5 year ERC research grant. Superconductivity in hydrogen sulphide, lanthanum hydride, and yttrium hydride were discovered recently with maximum transition temperatures between 200K and 260K at very high pressures above 100 GPa (1 million bar).
The PhD project focuses on transport measurements to characterise the superconductivity. This will include electrical resistivity, Hall effect and spectroscopic measurements. These will allow to map the phase diagram, and to study the normal and superconducting properties as a function of pressure. This insight will be important to understand and improve high-Tc superconductivity.
High pressures are generated with diamond anvil pressure cells readily available. The project is supported by two postdocs with more than 10 years experience in high-pressure research.
Most of the work is carried out at the University of Bristol. Some measurements take place at national and international facilities like the European High Magnetic Field lab in Nijmegen, NL.
Contact Dr Sven Friedemann for further details.
Diamonds pressing on a sample
Collective Spin and Charge Excitations in Superconductors and Other Novel Systems
Strong correlations between electrons in solids can lead to some spectacular effects, perhaps the most astonishing of which is high temperature superconductivity. The field of correlated electron systems has been made rich and exciting by a series of experimental discoveries over the last two decades. In this project you will investigate electronic order and the associated collective excitations. The aim of the research is to explain physical properties of materials such as superconductivity, electronic nematic order or charge order by measuring the electronic correlations. The work involves neutron and x-ray scattering, laboratory measurements using high magnetic fields and low temperatures, crystal growth and theoretical modelling. We carry out experiments at synchrotrons and neutron facilities around the around the world.
Two examples of materials which we are presently working on are the large temperature superconductor YBa2Cu3O6+x where we have recently observed charge order  and the 4d oxide metals Sr2RuO4 and Sr2Ru3O7  (see Figure).
Contact Professor Stephen Hayden for further details.
RIXS Studies of Spin, Charge and Lattice Correlations in Cuprate Superconductors
Unconventional superconductors and other quantum materials glean their unique properties from the interplay between the collective excitation of spin, charge and the crystal lattice. This project is to study these excitations and correlations using scattering techniques. Collective excitations have traditionally been studied using neutrons scattering and non-resonant x-ray scattering. However, resonant inelastic x-ray spectroscopy (RIXS) is a new and extraordinarily powerful tool which can probe spin excitations, charge excitations, phonons, and their mutual coupling. In this project we will use the state of-the-art (resonant inelastic x-ray spectroscopy) RIXS i21 facility at Diamond, together with other neutron and x-ray facilities to investigate novel and topical quantum materials such as the cuprate superconductors La2-xSrxCuO4, YBa2Cu3O6+x, Bi2Sr2-xLaxCuO6+x and correlated electron systems such as ruthenates and nickelates. The aim is to determine how the excitations mentioned above are related to the physical properties of these systems and to develop the RIXS as a probe of novel electronic materials by making quantitative comparisons with theory.
Spin excitations and phonons measured by RIXS in La2-xSrxCuO4 (Robarts et al 2019)
Electrochemical STM of Layered Chalcogenides
Layered chalcogenides are attracting considerable attention due to their unique properties. For example, bismuth chalcogenides such as Bi2Se3 or Bi2Te3 are model topological insulators and promising thermoelectric materials. Our group is pioneering the use of electrochemical STM to probe the nanoscale surface electrochemistry of layered chalcogenides in-situ.
A PhD position is available in this field. During the PhD, in-situ growth studies will deliver new insight into chalcogenide electrodeposition, which is of interest as a low-cost alternative to vacuum processes. Further in-situ studies will modify the electronic structure of layered compounds by molecular adsorption, which is of especial interest for future device applications. Also, some layered chalcogenides are very promising electroctalysts for water electrolysis, a process that uses electrical energy (ideally generated from renewable sources) to produce hydrogen fuel: in-situ electrochemical STM is the ideal way to probe their properties, especially the role of defects.
Contact Professor Walther Schwarzacher for further details.
Sn0.01Bi1.99Te2Se surface imaged in-situ, showing defect decoration following electrochemical dissolution and redeposition
Ice Nucleation in Aerosols Containing Biomolecules
By modifying how water droplets freeze, heterogeneous nucleating agents (HNAs) in clouds play a significant role in determining cloud reflectivity as a function of wavelength and therefore how different types of cloud contribute to global warming. Biomolecules including proteins can act as HNAs for ice. For example, plant pathogens are known to produce extremely efficient ice nucleating proteins, and even proteins that have not evolved specifically for this purpose, such as the iron storage protein ferritin which is produced by almost all living organisms, can be very effective HNAs. However, the factors that make proteins effective HNAs remain unclear.
The aim of the PhD project is to use model biomolecules, including ferritin and virus capsids, to study ice nucleating efficiency as a function of size, geometry and surface chemistry. During your PhD you will have further opportunities to improve your understanding of atmospheric ice nucleation and its environmental relevance through modelling and engagement with our project partners in the British Antarctic Survey.
This PhD is available through the EPSRC Centre for Doctoral Training in Aerosol Science. Contact ontact Professor Walther Schwarzacher for further details.
Arctic Ocean ice floes
Heavy Elements for Superspintronics
Materials with large spin-orbit interactions are of great interest in the field of spintronics, where they are used to generate spin-polarised currents via the spin Hall effect, and switch magnetic elements for memory and logic applications. At the same time in the field of superconductivity, spin-orbit interactions create Cooper pairs which are no longer simply spin singlet, but possess a triplet pair component with spins parallel. Combining these two fields, an area known as superspintronics, is of intense fundamental and practical interest, since the triplet Cooper pairs can exist inside neighbouring ferromagnetic layers in a thin film heterostructure, offering the opportunity of creating spintronic devices with greatly reduced ohmic losses.
In this context, elemental uranium, the heaviest naturally occurring element, is not only superconducting, but shows a range of spin-orbit strengths depending on its crystallographic character. In Bristol we have a thin film sputtering system, unique in the UK, capable of creating not only novel crystalline states of uranium in single crystal form, but also creating high quality heterostructures with ferromagnets and other materials. This project will leverage this equipment to investigate the low temperature properties of various U-based heterostructures and alloys to create novel electronic states of material and superspintronic devices.
Contact Dr Chris Bell for further details.
Schematic of triplet and singlet Cooper pairs (blue arrows indicate the electron spin moments) in a heavy element superconductor next to a ferromagnetic (black arrows are the aligned spins in the ferromagnetic). The triplet pairs can easily enter the ferromagnet, creating a superconducting ferromagnet with spin polarised supercurrent.
- Fully funded 3.5/4 year studentships through Doctoral Training Partnerships (DTPs), formally known as DTAs
- A fully funded 3.5 year studentship as part of an ERC research grant: PhD Advert Hydrides (PDF, 256kB)
- A fully funded 3.5 year studentship as a joint position at the University of Bristol and at the synchrotron at the diamond light source
- Fully funded 4 year studentships are available through the Centre for Doctoral Training in Aerosol Science
- Fully funded studentships up to 4 years through the China Scholarship Council – University of Bristol Joint Scholarships Programme