PhD Opportunities and Other Vacancies

This project is supported through the NAME EPSRC Programme grant on equivalent terms to the standard EPSRC doctoral training award – 3 ½ years stipend and fees.

Information in most electrical circuits is conveyed by charges that generate heat when they move round the elements of circuit.  Reducing the heat in IT systems is now such an important problem that a huge research effort is currently underway to find a solution. Traditionally, cooling has been the way we deal with heat, but this only increases the total energy requirements and so is damaging to the environment and is unsustainable.  A better solution would be to avoid generating so much heat in the first place so an alternative to encoding information in charges is a laudable goal. Here we are investigating using a pure spin current that transfers angular momentum (spin) without an accompanying charge current as a means to  transfer information without generating Joule heat.

In this project we will create pure spin currents by collecting spins at the interface between a ferromagnet and a normal metal.  This accumulation of spins generates spin-dependent potentials that drive the spins down the normal metal wire where they can be collected and detected.  There is no charge current in the wire because the up- and down-spins flow in opposite directions in equal numbers so there is no net current.  It turns out that the spin currents can be beneficially influenced by impurities that are deliberately put into the wire, but it matters where the impurities are deposited.

This project is part of a collaboration called NAME (https://name-pg.uk): Nanoscale Advanced Materials Engineering an EPSRC Programme Grant that aims to revolutionise the design and delivery of functionality on demand at the nanoscale within advanced materials.  The Universities of Manchester, Leeds and Imperial College and a number of industrial partners have come together to work on an exciting programme of research using the pooled resources and expertise of this world-leading group, enabling us to do more than any single laboratory could achieve.  You will work with a number of students and PDRAs not only in Leeds (1 student and 2 PDRAs) but across the collaboration acquiring an enhanced level of knowledge and skills.

Central to the project will be the P-NAME tool based in Manchester.  It is an atomic level ion implantation instrument with a 20nm resolution and is thus able to deposit impurities with unrivalled precision.   We will use impurities deposited in appropriate locations (on the surface, in the centre of the wire, etc) to influence the spin-orbit interaction of electrons in the wire and hence their spin properties.  You will grow lateral spin valves (10.1103/PhysRevLett.127.035901, 10.1103/PhysRevB.92.220420) in our bespoke MBE system and learn to make spin current transport measurements as a function of magnetic field and temperatures down to mK.  Working with the team in Manchester you will design a doping regime and characterise the impact of the deposition on your samples with the aim of increasing the spin signals in your transport measurements.  As a PhD student you will learn advanced materials deposition and characterisation, cleanroom fabrication, and Condensed Matter Physics measurement techniques applicable to a wide range of physics.  Our labs are just opening in the new Bragg laboratory at Leeds and are therefore state-of-the-art providing you with an ideal platform to launch your research career.

Formal applications for research degree study should be made online through the University's website. Please state clearly in the research information section that the research degree you wish to be considered for is Enhancing Spin Signals in Pure Spin Currents  as well as Dr Gavin burnell and Prof B J Hickey as your proposed supervisor.

If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below).

As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.

• UK/EU/International: UK and EU
• Value: This project is one of the priority DTA projects of the School of Physics and funded by the University of Leeds. The studentship consists of the award of fees with a maintenance grant for 3.5 years. It is also open to self-funded students and is eligible for funding in an open competition across the School of Physics, see funding schemes for details.
• Number of awards: 1
• Deadline:  11th February 2022

Supervisor(s)

Dr Satoshi Sasaki. Contact Satoshi Sasaki to discuss this project further informally.

Project description

Topological insulators are an existing class of band-gap insulators, whilst they do conduct through their edge (or the surface in the case of 3 dimensional materials). These gapless metallic surface states are naturally generated with helically-polarized spin texture due to strong spin-orbit coupling with a peculiar energy band structure of materials. Moreover the states are protected by time-reversal symmetry simply due to prohibition of back scattering and realize almost dissipationless pure spin currents (no net charge current) at the edge (surface) of materials. Spin-current devices based on the topological insulators save energy because it requires small current that flow at the edge (the surface) not in the bulk to access their surface properties.

In this project, we will fabricate a spin-current field effect transistor with an ultra-thin topological insulator Bi2-xSbxTe3 film1 grown by molecular beam epitaxy in ultrahigh vacuum, a part of a new multi-deposition system in Leeds. Existence of gapless states in topological insulators are one of peculiar characteristics but we will open a gap in the surface state by employing ultra-thin films where the top and bottom surface states get unstable due to an interference between two. The gapped surface state with a gating technique will provide us a capability of fabricating a spin-current filed effect transistor that can switch on/off the spin-polarized current. We will also keep our eye on other topological insulator materials suitable for this device project.

This is a project in an exciting and very active research area which allows us to closely interact and collaborate with other research teams in the University of Leeds including a theoretical group. We are looking for a motivated student with a background in physics, physical chemistry, or material science.

Entry requirements

Applications are invited from candidates with or expecting a minimum of a UK upper second class honours degree (2:1), and/or a Master's degree in physics or a related subject.

If English is not your first language, you must provide evidence that you meet the University's minimum English Language requirements.

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is the 'Ultra-thin topological insulator spin-current transistor' as well as Dr Satoshi Sasaki as your proposed supervisor.

Our department is proud to create inclusive student, research, and working cultures that are supportive and welcoming to those from all backgrounds, genders, ages, disabilities, religions, and other protected groups. We are committed to providing a postgraduate program that not only equips you with the technical and professional skills you will need in your career, but which is also enjoyable, supportive, diverse, and inclusive. We welcome all applications, but especially those from the under-represented groups in physics. Everybody’s needs will be supported, but if you do have any concerns, you can contact us, in confidence, to discuss how we can support your particular needs during a research degree at the University of Leeds.

If you require any further information please contact the Graduate School Office, e: maps.pgr.admissions@leeds.ac.uk

• UK/EU/International: UK and EU
• Value: Diamond Studentship funded jointly by Diamond Light Source and the University of Leeds. This includes UK/EU fees (£4,400 Session 2018/19 rate), student stipend (£17,777 Session 2018/19 rate) and funding for travel/accommodation between Diamond and Leeds at a rate of £2,000 p.a. for 3.5 years.
• Number of awards: 1
• Deadline: 3 May 2019

Supervisor(s)

Dr Thomas Moore, Dr Sarnjeet Dhesi, and Dr Francesco Maccherozzi. Contact Thomas Moore to discuss this project further informally.

Project description

There has been an explosion of interest in skyrmions in recent years, with the very first x-ray images of skyrmion dynamics being released recently. Skyrmions exist in magnetic thin films as nanoscale whirls of magnetization. Their topological stability, nanoscale size and potential for energy-efficient manipulation means that they are being actively developed for technological applications.

In this project, electron microscopy combined with intense polarised x-rays in a PhotoEmission Electron Microscope (PEEM) will be used to image skyrmions and their dynamics in thin magnetic films under strain. A major avenue of the research will involve manipulating skyrmion shape via strain from a piezoelectric transducer which significantly affects their magnetization dynamics. The aim of this project is then to understand how static or impulsive strain influences skyrmion dynamics using the high-resolution magnetic imaging capabilities of the PEEM housed at the UK national synchrotron facility (Diamond Light Source, Oxfordshire).

The ultimate goal is to build computing components, such as neural networks, that use skyrmions under strain as key functional parts. The project will begin at Leeds with the nanofabrication of arrays of magnetic thin film disks containing skyrmions, which will be placed on a piezoelectric transducer. A substantial part of this project is based at Diamond Light Source where magnetic imaging using the PEEM will be developed to understand novel skyrmion spin textures under strain. The work at Diamond Light Source will also involve developing the capability of a new aberration-corrected PEEM which will allow imaging skyrmion spin textures at the highest spatial resolution available.

Links: University of Leeds Condensed Matter Group, Diamond Light Source, Beamline I06, Diamond Light Source

Entry requirements

Applications are invited from candidates with or expecting a minimum of a UK upper second class honours degree (2:1), and/or a Master's degree in physics or a related subject.

If English is not your first language, you must provide evidence that you meet the University's minimum English Language requirements.

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is the 'Skyrmions under strain' as well as Dr Thomas Moore as your proposed supervisor.

Our department is proud to create inclusive student, research, and working cultures that are supportive and welcoming to those from all backgrounds, genders, ages, disabilities, religions, and other protected groups. We are committed to providing a postgraduate program that not only equips you with the technical and professional skills you will need in your career, but which is also enjoyable, supportive, diverse, and inclusive. We welcome all applications, but especially those from the under-represented groups in physics. Everybody’s needs will be supported, but if you do have any concerns, you can contact us, in confidence, to discuss how we can support your particular needs during a research degree at the University of Leeds.

If you require any further information please contact the Graduate School Office, e: maps.pgr.admissions@leeds.ac.uk

• UK/EU/International: Worldwide (International, UK and EU)
• Value: This project is open to self-funded students and is eligible for funding in an open competition across the School of Physics, see funding schemes for details.
• Number of awards: 1
• Deadline: Applications accepted all year round

Supervisor(s)

Contact Professor Christopher Marrows to discuss this project further informally.

Project description

Frustration is the inability of a physical system to simultaneously satisfy competing constraints. It occurs across physics and beyond, but is a particularly important topic in magnetism, a field in which (relatively) simple systems can be represented by toy statistical mechanical models that can then be extended into other fields model phenomena as diverse as forest fires and financial networks.

The study of frustration in magnetism has recently been given a new lease of life since artificial frustrated systems can now be built and studied using nanotechnology: in the case of magnetism, this is done by constructing arrays of magnetic nanoelements arranged in patterns where their magnetostatic interactions are frustrated.

The advantages of this approach is that it is possible to build experimental realisations of models that nature does not provide crystal structures for, with every parameter in the model tunable by adjusting the element size, shape, and spacing. Moreover, the microstates of these artificial statistical mechanical systems can be inspected in detail using advanced magnetic microscopy methods, including time-resolved imaging to study thermal fluctuations in those microstates.

To date, almost all artificial frustrated spin systems have been ‘crystalline’ in that they are periodic arrays. In particular, square and hexagonal arrays have been studied as analogs of spin ice crystals. Thermal excitations in spin ices show appear as emergent quasiparticles with many of the properties of magnetic monopoles, physics that has been reproduced in their artificial counterparts. In this project we will study quasicrystalline systems, where the magnetic nanoelements are arranged on a Penrose tiling. Whilst small parts of this pattern repeat, the whole pattern never does.

We have begun to study these Penrose-based systems in an athermal state, where the energy scales are all much larger than kT and so the state of the system is frozen in. In this project we will build systems that are thermally fluctuating by tuning these energy scales towards kT. In this way we will study collective nature of the freezing and melting of the artificial spin system and seek to understand the nature of its emergent excitations.

Entry requirements

Applications are invited from candidates with, or expecting, a minimum of a UK upper second class honours degree (2:1) in a relevant discipline, a Master's degree in a relevant discipline, or both.

If English is not your first language, you must provide evidence that you meet the University’s minimum English Language requirements.

Additional staff contact

Gavin Burnell

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is 'Fluctuation and equilibration in artificial magnetic quasicrystals' as well as Professor Christopher Marrows as your proposed supervisor.

Our department is proud to create inclusive student, research, and working cultures that are supportive and welcoming to those from all backgrounds, genders, ages, disabilities, religions, and other protected groups. We are committed to providing a postgraduate program that not only equips you with the technical and professional skills you will need in your career, but which is also enjoyable, supportive, diverse, and inclusive. We welcome all applications, but especially those from the under-represented groups in physics. Everybody’s needs will be supported, but if you do have any concerns, you can contact us, in confidence, to discuss how we can support your particular needs during a research degree at the University of Leeds.

If you require any further information please contact the Graduate School Office, e: maps.pgr.admissions@leeds.ac.uk

• UK/EU/International: Worldwide (International, UK and EU)
• Value: This project is open to self-funded students and is eligible for funding in an open competition across the School of Physics, see funding schemes for details.
• Number of awards: 1
• Deadline: Applications accepted all year round

Supervisor(s)

Contact Professor Christopher Marrows to discuss this project further informally

Project description

In this project we will study magnetic skyrmions, nanoscale swirls of spins that possess a special topology. They appear in properly designed magnetic multilayers at room temperature and are candidates for next-generation data storage technology. It is now over a decade since the carbon footprint of the internet grew larger than that of commercial air travel, much of this energy is used to physically spin hard disks, write data to them, and write and refresh volatile memory. To drive skyrmions along a crystal using spin torque requires several orders of magnitude less current density then driving magnetic domains under ideal conditions, but this is not seen in practice in these systems so far. Magnetic skyrmions offer the prospect of vastly reducing the energy needed to write and store digital data if their properties can be controlled.

In Leeds we have a rich programme of research on skyrmions carried out with several leading European laboratories in France, Germany and Switzerland. Potential topics for PhD study include studying the thermal stability of skyrmions in order to establish their reliability as a store of digital data (arXiv:1706.01065 [cond-mat.mes-hall]), studying their transport properties as a means of electrically detecting them (arXiv:1706.06024 [physics.app-ph]), and the mobility of skyrmions at room temperature under the influence of the torques exerted by spin-polarised currents.

Entry requirements

Applications are invited from candidates with, or expecting, a minimum of a UK upper second class honours degree (2:1) in a relevant discipline, a Master's degree in a relevant discipline, or both.

If English is not your first language, you must provide evidence that you meet the University’s minimum English Language requirements.

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is 'Magnetic skyrmions in chiral multilayers' as well as Professor Christopher Marrows as your proposed supervisor.

Our department is proud to create inclusive student, research, and working cultures that are supportive and welcoming to those from all backgrounds, genders, ages, disabilities, religions, and other protected groups. We are committed to providing a postgraduate program that not only equips you with the technical and professional skills you will need in your career, but which is also enjoyable, supportive, diverse, and inclusive. We welcome all applications, but especially those from the under-represented groups in physics. Everybody’s needs will be supported, but if you do have any concerns, you can contact us, in confidence, to discuss how we can support your particular needs during a research degree at the University of Leeds.

If you require any further information please contact the Graduate School Office, e: maps.pgr.admissions@leeds.ac.uk

• UK/EU/International: Worldwide (International, UK and EU)
• Value: This project is open to self-funded students and is eligible for funding in an open competition across the School of Physics, see funding schemes for details.
• Number of awards: 1
• Deadline: Applications accepted all year round

Supervisor(s)

Contact Dr Gavin Burnell to discuss this project further informally.

Project description

Superconducting computers operating at 4.2K have been proposed to solve the problems of energy usage by large-scale computing, and interfacing a quantum computer operator at mili-Kelvin temperatures with conventional room temperature electronics. Whilst the technology to implement logic in such a 4.2K computer is well established, there remains, as yet, no suitable technology to implement cryogenic memory. We are aiming to address this need by developing the physics and materials to implement memory technologies based on superconductor-ferromagnetic Josephson junctions.

A ferromagnetic Josephson junction combines elements from magnetic RAM where data is stored in the magnetic configuration of magnetic tunnel junction with the low dissipation/ low voltage readout inherent in a superconducting Josephson junction. The primary challenges that are to be overcome in realizing this concept are to develop on-chip methods of writing the data - either through local magnetic field control or preferably through direct electrical writing of the magnetic state via spin-transfer-torque.

This project will build on our most recent publication [1] we have demonstrated a proof of concept device combining a perpendicular magnetic anisotropy spin-valve with a Josephson junction to produce a device with a controllable 60% change in critical current for two different magnetic states.

[1] Satchell N, Shepley P M, Algarni M, Vaughan M, Darwin E, Ali M, Rosamond M C, Chen L, Linfield E H, Hickey B J and Burnell G 2020 Spin-valve Josephson junctions with perpendicular magnetic anisotropy for cryogenic memory Appl. Phys. Lett. 116 022601

Entry requirements

Applications are invited from candidates with, or expecting, a minimum of a UK upper second class honours degree (2:1) in a relevant discipline, a Master's degree in a relevant discipline, or both.

If English is not your first language, you must provide evidence that you meet the University’s minimum English Language requirements.

Additional staff contact

Prof. Christopher Marrows
Prof. B.J. Hickey

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is 'Fluctuation and equilibration in artificial magnetic quasicrystals' as well as Professor Christopher Marrows as your proposed supervisor.

Our department is proud to create inclusive student, research, and working cultures that are supportive and welcoming to those from all backgrounds, genders, ages, disabilities, religions, and other protected groups. We are committed to providing a postgraduate program that not only equips you with the technical and professional skills you will need in your career, but which is also enjoyable, supportive, diverse, and inclusive. We welcome all applications, but especially those from the under-represented groups in physics. Everybody’s needs will be supported, but if you do have any concerns, you can contact us, in confidence, to discuss how we can support your particular needs during a research degree at the University of Leeds.

If you require any further information please contact the Graduate School Office, e: maps.pgr.admissions@leeds.ac.uk