Academic projects search

Transition metal oxides host a wide range of physical properties and functionalities, making them an ideal platform for implementing potential future devices. The aim of this project is to establish novel ways to manipulate the local properties of transition metal oxides by using a scanning tunneling microscope to enable writing device structures at the atomic scale into the surface of the material. To establish the properties of these written device structure, you will first use scanning tunneling spectroscopy, but later also explore possibilities to contact the written structures macroscopically to study transport through these and enable actual device operation. While initial studies will be performed on bulk material, at later stages of the project, thin-film samples grown by reactive oxide molecular beam epitaxy will be used.

In many unconventional superconductors, magnetism and superconductivity occur in close proximity to each other - which is surprising given that they are usually considered mutually exclusive properties of a material. This is also true for the iron pnictide superconductors, where in several materials magnetism and superconductivity appear to coexist from macroscopic measurements. In this project, you will take an atomic scale view at the magnetic order and the superconducting properties using low temperature spin-polarized scanning tunneling microscopy[1]. Combining images of the magnetic order with a characterization of superconductivity from tunneling spectroscopy will allow to establish whether magnetism and superconductivity coexist microscopically, or whether they are really competing. These results provide important benchmarks for theory, and may help to establish an understanding of superconductivity in these materials.

You will be using bespoke low temperature scanning tunneling microscopes, which are installed in a new ultra-low-vibration facility at the University of St Andrews.

[1] Enayat et al., Science 345, 653 (2014)

The aim of this project is to investigate experimentally the influence of broken inversion symmetry on superconductivity in a variety of non-centrosymmetric (NCS) materials. Most crystalline metals have a structure that maps onto itself exactly under inversion of spatial coordinates. Such materials are termed “centrosymmetric” and when they become superconducting, the spatial part of the Cooper pair wavefunction must have a definite parity, i.e. inversion simply multiplies it by ±1. This imposes restrictions also on the spin configuration within the Cooper pair. By contrast, in non-centrosymmetric superconductors where the crystal structure breaks inversion symmetry, such restrictions do not apply. Amongst the properties predicted for non-centrosymmetric superconductors are mixed spin-singlet/spin-triplet pairing, enhanced critical fields and spatially modulated superconducting states. Whilst unusual superconducting properties have been detected in a number of NCS materials, there is relatively little firm experimental evidence linking these to the lack of inversion symmetry; for example only in very few cases has a substantial triplet component of the order parameter been firmly established.

The project will be focused on NCS superconductors where the electronic correlations are weak, since these offer the chance to isolate the role of the broken inversion symmetry. The experiments will focus on using low temperature scanning tunneling microscopy and spectroscopy to establish the structure of the superconducting order parameter and study the influence of defects of different dimensionalities on the superconducting properties.

Many quantum materials exhibit complex magnetic orders, which often are sensitive to external stimuli, such as magnetic field or doping, making them in principle interesting for many technological applications. Characterization of the spatial structure of the magnetic order has mostly been done through Neutron scattering, which however average over a macroscopic sample volume. Spin-polarized scanning tunneling microscope provides real space images of magnetic order at the atomic scale, thereby providing new insights into the spatial structure of the complex magnetic orders. In this project, you will use low temperature scanning tunneling microscopy in a vector magnetic field to characterize the magnetic structure of quantum materials. The studies will aim to establish the surface impact on the magnetic order, knowledge which is critical for technological exploitation and interfacing to other materials, but also to provide a microscopic picture of the magnetic order which will help to identify the dominant contributions to the magnetic interactions in the material. We are in particular interested in metamagnetic phases, where the external magnetic fields can drive phase transitions in the material.

You will be using bespoke low temperature scanning tunneling microscopes, which are installed in a new ultra-low-vibration facility at the University of St Andrews.

[1] Enayat et al., Science 345, 653 (2014).
[2] Singh et al., Phys. Rev. B 91, 161111 (2015).
[3] Trainer, et al., Rev. Sci. Instr. 88, 093705 (2017).

We are seeking an ambitious and motivated PhD student to join an EPSRC-funded project which seeks the adventurous goal of "designer magnetism", based around the flexibility and functionality offered by 2D magnetic materials. Of fundamental importance in its own right, but also as a platform to create targeted spintronic functionality, interfacing different van der Waals materials and magnets together promises almost limitless possibilities for tuning magnetic interactions and ordering tendencies and for realising new quantum states and phases. 
You will join an EPSRC-funded project which is working to develop an integrated approach to achieve this via the synthesis and spectroscopic characterisation of such 2D magnetic van der Waals heterostructures. We seek a PhD student to focus on advancing the spectroscopic investigation of these systems, probing their electronic structure in both k-space and real space, and developing routes to probe their magnetic order and excitations on the atomic scale. This project will make extensive use of the unique integrated materials synthesis and spectroscopy (STM, spin- and laser-ARPES) facilities of the Centre for Designer Quantum Materials in St Andrews, and builds on the host groups' experience in the study of 2D materials, of atomic-scale magnetic imaging, and of understanding and modelling their electronic structures [e.g. 1-5]. We seek a candidate who is interested to work collaboratively within and between these groups. 
For further information, or to discuss specific research possibilities, please contact pdk6@st-andrews.ac.uk or gpw2@st-andrews.ac.uk.

[1] Kushwaha et al. arXiv:2409.00189 (2024)
[2] Feng et al., Nano. Lett. 18 (2018) 4493
[3] Enayat et al., Science 345 (2014) 653
[4] Riley et al., Nature Physics 10 (2014) 835
[5] Edwards et al., Nature Materials 22 (2023) 459

This project would be eligible for funding including: EPSRC DTP (Must be within EPSRC remit.)

• The Centre for Designer Quantum Materials