Hydride high-temperature superconductors
A position is available to study record superconductors in a joint research project between the University of Bristol and Diamond Light Source synchrotron facility.
Record superconductivity with transition temperatures to above zero Celsius have been discovered in hydride compounds at high pressures in the last 5 years including LaH10, YH9, SH3, and carboneous sulphur hydride. This highlights the potential of conventional superconductivity. Indeed, conventional superconductors have the advantage that theory successfully guides experiment to find new materials with higher Tc whilst for unconventional superconductors such a theoretical framework remains elusive. In this project we will establish experimental evidence for the relationship between structure and superconducting properties in hydride superconductors and use this to find better superconductors.
An important part of the work will be to control the synthesis at high pressures inside a diamond anvil cell with laser heating at high pressures. The project includes developments for accurate temperature measurement and control at the beamline I15 and at the University of Bristol. We will synthesise hydride superconductors with the highest prospect for high-temperature superconductivity and study the relation between structure and electronic properties of individual samples. We will tune superconductivity via control of electron and hole doping in LaHx and YHx and will probe ternary hydrides like Li2MgH16 and YCaH12 with highest predicted Tc.
Supervisors: Dr Simone Anzellini from Diamond Light Source, Dr Sven Friedemann and Dr Oliver Lord from University of Bristol
You will work alongside other PhD students, post-doctoral research assistants, and with the project supervisors. The project is also supported by funds from the European Research Council and the Engineering and Physical Research Council.
Please contact Sven Friedemann(Sven.Friedemann@bristol.ac.uk) for further details. Further details are available from the website of the Diamond Light Source. You can apply at http://www.bristol.ac.uk/study/postgraduate/apply/. Please select School of Physics as department and include Sven Friedemann as a contact person for the project. Applications will remain open until a suitable candidate is appointed.
Diamonds in a high-pressure cell.
Heavy fermion thin films
Bulk crystals can display heavy fermion behaviour, where the effective mass of mobile carriers can be up to 1000 times larger than the bare electron mass due to electron-electron interactions. Many of these materials are U-based compounds, such as UGe2 and UPt3, and they also display a range of other fascinating physics including unconventional superconductivity, quantum criticality and magnetism [1, 2]. The ability to grown such materials as thin films opens up a range of interesting possibilities: (i) we can explore the effect of dimensionality by tuning the film thickness; (ii) apply compressive and tensile strains using different crystalline substrates to tune the emergent physics; (iii) we can create more complex structures such as superlattices and device architectures to interrogate the system in novel ways. While there have been a few studies in these directions [3-5] there is a vast range of opportunities open to explore.
In Bristol we have a thin film sputtering system, unique in the UK, capable of growing compounds of uranium in high quality single crystal form [6,7]. This project will leverage this equipment to investigate the growth and low temperature properties of various U-based compounds in the search for novel tuning parameters to control heavy fermion behaviour, superconductivity and magnetism in these materials.
Supervisors: C. Bell & R. Springell
Figure: Schematic of tuning heavy fermion thin films with epitaxial strain (horizontal axis) and finite size (diagonal axis).
 Saxena et al., Nature 406, 587 (2000)
 Joynt & Taillefer, Rev. Mod. Phys. 74, 235 (2002)
 Jourdan et al., Nature 398, 47 (1999)
 Jourdan et al., Phys. Rev. Lett. 93, 097001 (2004)
 Mizukami et al., Nat. Phys. 7, 849 (2011)
 Bright et al., Thin Solid Films 661, 71 (2018)
 Bao et al., Phys. Rev. B 88,134426 (2013)
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)
Electrodeposited nano-structured coatings for nuclear industry applications
Electrodeposition can deliver high quality nano-structured coatings at very low cost. It operates at ambient temperatures and pressures, and has the further advantage that it can coat components with complex geometries, because deposition takes place wherever the surface is exposed to electrolyte. This project will explore the deposition, radiation tolerance and corrosion resistance of nano-crystalline, amorphous and compositionally modulated electrodeposited films with thicknesses up to a few tens of µm.
Our reference material will be electrodeposited nanocrystalline Ni prepared using well-established pulse plating techniques. For the purposes of comparison with nanocrystalline coatings, we shall also electrodeposit amorphous Co-P and Co-W. Even when both alloys are amorphous, the radiation tolerance of Co-W could be enhanced because W is a much heavier atom. In a key part of this project, we shall then electrodeposit artificially layered materials in which the total thickness can be as high as 10s of µm, but the individual layer thicknesses are down to a few nm. Layering is expected to provide an effective barrier to damage propagation, and this study could provide unique insight into the mechanisms of radiation damage and corrosion resistance in nano-structured metals. Pulse electrodeposition from a single-electrolyte, a technique in which Bristol has internationally leading expertise, will be used to produce Ni-Cu multilayers with different repeat distances in the sub-nm to few-nm range to establish how boundary spacing affects coating properties. A PhD position is available in this field.
Contact Professor Walther Schwarzacher for further details.
Example of an electrodeposited nano-structure: a nanowire consisting of alternating ferromagnetic and non-magnetic layers imaged by transmission electron microscopy
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.
Crystal Structure of Sr3Ru2O7
- 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.
- 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 studentships up to 4 years through the China Scholarship Council – University of Bristol Joint Scholarships Programme