Quantum materials

Arzhang Ardavan

Molecular magnets are a class of zero-dimensional strongly correlated electron systems exhibiting a highly coherent quantum spin at low temperatures. By varying the molecular structure, properties of the spin such as its moment, anisotropy, etc, can be manipulated in a controlled way, offering a beautiful playground for experiments in quantum magnetism.

This project will investigate ways of exploiting the quantum properties of molecular magnets with a range of objectives. Through close collaborations with chemists who synthesise the materials, we will design structures using molecular spins as qubit candidates. In simple multi-qubit structures, we will use state-of-the-art electron spin resonance equipment to generate entangled states and perform basic quantum information algorithms. We will also develop new ways of measuring electrical transport through single molecules using innovative methods for device construction, and scanning tunnelling microscopy (via collaboration with IBM).

Stephen Blundell

A muon is a spin-1/2 particle. When implanted in a solid, the muon behaves as a microscopic magnetometer. This is because its spin can precess in the local magnetic field. In various frustrated magnets it is possible for muons to probe low-frequency spin dynamics. By combining muon-spin rotation experiments and a.c. susceptibility one can learn a lot about these slow fluctuations which are known to persist to low temperature. But are these so-called “persistent spin dynamics” an intrinsic effect, or are they a highly subtle artefact of the muon implantation process? This project is designed to find out.

Stephen Blundell

The Nicholas Kurti High Magnetic Field Laboratory in the Clarendon Laboratory is capable of producing the highest magnetic fields for condensed matter physics experiments in the UK. This is achieved using pulsed magnetic fields which are short in duration and are a factor of 2 or 3 times higher than the ~20T limit set by superconducting magnets. This allows experiments in which quantum magnets are pushed into new regimes. Some of these quantum magnets are based on inorganic materials, but why not use molecules? This gives a much more flexible approach to understand low-dimensional quantum magnetism.

Stephen Blundell and Amalia Coldea

Magnetic fields are a unique tool to explore and tune quantum materials towards extreme experimental regimes in which new phases of matter can be stabilised. Additionally, magnetic fields are essential to characterise the phase diagram of novel superconductors to identify suitable candidates for practical applications. This is an experimental project to explore and develop new experimental techniques for studying quantum materials in ultra-high magnetic fields. The quantum materials to be explored will include novel iron-based superconductors and molecular magnets, as well as systems in which the spin, electronic and lattice degrees of freedom interact strongly and can be disturbed by a magnetic field.

The student will be combining transport and thermodynamic techniques using superconducting magnets and pulsed field magnets available in Oxford. The pulsed magnetic fields are short in duration but up to a factor of 3 times higher than the field produced by superconducting magnets. Oxford has a long tradition in high magnetic field research having the largest magnetic fields in the UK for condensed matter physics both using pulsed field in the Nicholas Kurti High Magnetic Field Laboratory as well as superconducting magnets up to 21T as part of the High Magnetic Field facilities and the new Oxford Centre for Applied Superconductivity.

A suitable candidate needs to have a good understanding of condensed matter physics and good computational skills as well the ability to work well in an experimental team. The student will be co-supervised by Professor Stephen Blundell and Professor Amalia Coldea.

Andrew Boothroyd

In the last decade, solids called topological quantum materials have become a hot topic with the discovery of electronic states in crystalline solids which are topologically distinct from those of electrons in free space. Topological metals and semimetals exhibit exceptional transport behaviour due to the existence of low-energy quasiparticles which resemble relativistic fermions, and are very promising for practical applications.

In this project you will investigate materials in which the topology of the electrons can be controlled by magnetic order or magnetic fields. These materials take the form of crystalline solids containing magnetic atoms such as manganese, iron and europium, which are responsible for the compound’s magnetism.

The project will combine experimental work with theoretical modelling and numerical analysis to interpret the data. You will perform neutron scattering and magnetic x-ray scattering experiments at international condensed matter facilities in the UK and overseas to probe structure and dynamics on the atomic scale. These experiments will directly determine the magnetic ground states and excited states of the electrons, and by doing so you will gain an understanding of the interactions that stabilise the exotic electronic phases. You will also study the bulk properties of materials, such as their magnetic susceptibility, resistivity and heat capacity, using state-of-the-art facilities in the Clarendon Laboratory.

For more information, contact: andrew.boothroyd@physics.ox.ac.uk

Andrew Boothroyd

This project is concerned with the investigation of magnetic phenomena in unconventional superconductors by neutron scattering and resonant x-ray scattering techniques.

In conventional superconductors, superconductivity is understood to be a condensation of electron pairs (“Cooper pairs”) with zero orbital angular momentum and a singlet spin state. Superconductors are termed “unconventional” if the electron pairs have a non-trivial orbital or spin angular momentum state. In the original BCS theory, the glue which induces electrons to form pairs is provided by phonons, and this mechanism accounts for many conventional superconductors. More recently, a variety of other pairing mechanisms have been proposed for unconventional superconductors, amongst which are mechanisms that involve magnetic fluctuations.

In this project you will investigate atomic-scale magnetism and associated structural and electronic correlations in unconventional superconductors through neutron and x-ray scattering experiments at condensed matter facilities in the UK and overseas. You will also study bulk properties of the materials, e.g. their magnetization and transport behaviour, using facilities in the department. You will perform experiments on a number of different types of unconventional superconductors and related materials, in particular iron-based superconductors and the recently discovered family of layered nickel oxide superconductors. The aim of the experiments will be to obtain high quality data with which to test theoretical models.

The project would suit students with skill in experimental work but also with an interest in data analysis and theoretical modelling. A willingness to work away from the host institution for short periods is also essential.

This project will be undertaken as part of the EPSRC Superconductivity Doctoral Training Centre, and will be in collaboration with Prof Stephen Hayden (University of Bristol).

For more information, contact Prof Andrew Boothroyd

Radu Coldea

We explore experimentally materials where quantum correlation effects between electrons are important and often lead to novel forms of electronic order or dynamics dominated by quantum effects. Of particular interest is the phenomenon of "quantum frustration", ie how quantum systems resolve competing interactions, this is explored in frustrated spin-, orbital- and charge-ordered systems. Another focus is "quantum criticality" when the transition temperature to spontaneous magnetic order can be suppressed by high magnetic fields all the way down to zero temperature, thus realising a regime where all ~10^23 electron spins in the material fluctuate strongly, but in perfect unison, a new regime for quantum matter that is only now becoming accessible experimentally and we plan to measure directly the quantum spin fluctuations via neutron scattering. The DPhil project will involve a mix of thermodynamic measurements, xray and neutron scattering experiments, data analysis and modelling.

JC Séamus Davis

2 x DPhil studentships are available from ERC (European Research Council)

The studentships are part of an European Research Council funded project entitled "MILLIKELVIN VISUALIZATION OF TOPOLOGICAL ORDER (mVITO)" being undertaken by the University of Oxford, UK and University College Cork, IE under PI JC Séamus Davis. The objective of this project is to develop and apply new techniques for atomic-scale visualization of electronic and magnetic quantum matter. Per interest and availability, the student will focus on one of the following sub-projects:

Visualisation of electronic wavefunctions in topological Kondo insulators or heavy fermion superconductors, using millikelvin scanning tunnelling microscopy.

Visualisation of Cooper-pair condensates or pair density wave states using scanned Josephson tunnelling microscopy.

Visualisation of classical and quantum spin liquids using scanned magnetic-flux microscopy.

S/he will be a member of the Davis Group and will be supervised by Professor JC Séamus Davis. Further information on the group and its research can be found here.

Prospective candidates will be judged according to how well they meet the following criteria:

Demonstrates curiosity, creativity and courage in scientific research.

• A first class honours degree in Physics or equivalent
• Experience in low temperature physics at liquid-helium temperatures T=4.2K or below
• Experience in ultra-high vacuum scanned probe microscopy
• Experience in high-volume image-data management and analysis
• Excellent English or Irish written and spoken communication skills

The following skills are desirable but not essential:

• Ability to program in Matlab and/or Python
• Ability in Labview-based experiment design and management
• Ability in cryogenic operations with liquid helium, and ultra-high vacuum tech
• Ability with modern theoretical techniques of quantum matter research

John Gregg

The end of Moore's Law has long been prophesied, but its effects have been subtly present for over a decade: since 2004, computer processor clock speeds have been frozen circa 4GHz, as a desperation measure to prevent heat death of the chips. As increasing functionality is packed at ever higher density into semiconductor devices, the resulting heat dissipation yields multiple issues: device unreliability; inability of battery technology to keep pace with the power demands of portable devices such as phones and tablets; and the enormous heat generation of "server farms" - performing 30 Google searches is claimed to dissipate enough heat to boil a kettle.

Alternative computing technology based on magnons (waves of propagating angular momentum that exist in ordered magnetic materials) offers an elegant and viable room temperature solution to these problems. Magnonic processors use 1/1000 of the power of their silicon counterparts, are engineerable on the nanoscale and have clock speed ceilings that are potentially in the TeraHertz. Sophisticated logic devices such as XOR gates and half adders have already been demonstrated as has a magnonic equivalent of the field effect transistor. Moreover, magnonic computing paradigms offer functionality and economy of "real estate" that is impossible with silicon, such as the ability simultaneously to perform different operations on parallel datastreams using the same hardware. Recent work by our team demonstrates magnonic ability to perform the operations of time reversal and phase conjugation with a view to combining the speed of analogue computing with the versatility of digital.The D.Phil. project here described will involve further developing this new microwave science and its integration into conventional electronic hosts.

Thorsten Hesjedal

Magnetic skyrmions are tiny, swirling spin structures with unique properties that make them promising candidates for future data storage technologies. These non-collinear magnetic systems exhibit a rich spectrum of excitations across a huge range of timescales, e.g., tied to the magnetic lattice dynamics or the internal dynamics of the spin textures. Recently, 3D versions of skyrmions have been discovered, revealing emerging physical effects with a tremendous application potential. The figure below shows in panel (a) the starting point of our exploration, at which it was believed that skyrmions are 2D objects that simply stack up to form tubes in 3D. In reality, near any surface, the skyrmion forms (b) twisted 3D structures which were first discovered using a technique developed by us, called CDREXS (= circular dichroism resonant elastic x-ray scattering). Over the past decade, we have developed (and applied) a suite of synchrotron-based magnetic characterisation techniques, built on the well-established x-ray magnetic circular dichroism (XMCD) effect, uniquely unravelling their topological static and mode- and layer-resolved dynamic properties (diffractive and reflectivity FMR = DFMR and RFMR), drawing from our development of time- and element-resolved x-ray detected FMR (XFMR). Using our CD-REXS technique, we also discovered (c) entangled 3D skyrmion structures, (d) chiral bobbers, which are terminated by monopoles, and we are keen to fully explore (e) magnetic Hopfion textures. 

This project is aimed at developing and utilizing advanced synchrotron-based techniques to explore the dynamics of these topological structures, achieving both the full reconstruction of their 3D magnetic structure as well as their time-dependent dynamics. 

The project will be jointly supervised by Prof Thorsten Hesjedal (Oxford) and Prof Gerrit van der Laan (Diamond Light Source), and the workplace will be the Harwell Science and Innovation Campus, which is home to Diamond Light Source.

Funding for the studentship has been applied for (funding decision March 2025) and is open to UK/Home fee students only.

Email   Prof Thorsten Hesjedal at: thorsten.hesjedal@physics.ox.ac.uk

            Prof Gerrit van der Laan at: Gerrit.vanderlaan@diamond.ac.uk

Paolo G Radaelli

A collaboration between Professor Paolo G. Radaelli and Professor Andrea Cavalleri, who holds a joint appointment between the Clarendon Laboratory and the Max Planck Institute for the Structure and Dynamics of Matter, (Hamburg).

The use of light to control the structural, electronic and magnetic properties of solids is emerging as one of the most exciting areas of condensed matter physics. One promising field of research, known as femto-magnetism, has developed from the early demonstration that magnetic ‘bits’ in certain materials can be ‘written’ at ultra-fast speeds with light in the visible or IR range [1]. More radically, it has been shown that fundamental materials properties such as superconductivity can be ‘switched on’ transiently under intense illumination [2]. Recently, the possibilities of manipulating materials by light have been greatly expanded by the demonstration of mode-selective optical control, whereby pumping a single infrared-active phonon mode results in a structural/electronic distortion along the coordinates of a second, anharmonically coupled Raman mode – a mechanism that was termed ‘nonlinear phononics’. Crucially, the Raman distortion is partially rectified, meaning that it oscillates around a different equilibrium position than in the absence of illumination. Recently it was realised that, under appropriate conditions, the rectified Raman distortion can transiently break the structural and/or magnetic symmetry of the crystal and hypothesised that such symmetry breaking would persist for a time corresponding to the carrier envelope of the pump, which can be less than a picosecond, and can give rise to the ultra-fast emergence of ferroic properties such as ferromagnetism and ferroelectricity [4]. Even more recently, this effect was experimentally demonstrated for the first time in our collaborators’ laboratory in Hamburg. Surprisingly, photo-ferroicity persisted for a significantly longer time than the carrier envelope (100s of ps). Although this is not yet fully understood, the most likely explanation is that magnetisation is being transferred to slower electronic/magnonic excitations.

This DPhil project will give the successful candidate the opportunity to pioneer this new field of research. Initial experiments on the ‘photo-ferroic’ materials that we have already characterised will be performed at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany. As a mode-selective pump, we are employing coherent laser radiation in the THz or far-IR range with sub-ps carrier envelopes, while the transient emergence of the ferroic properties will be probed with second-harmonic generation (SHG), Faraday rotation and dichroic absorption of visible/near-infra-red light. Later on in the project, changes in the crystal and magnetic structures of the materials will be probed with X-rays at free electron laser sources such as the European XFEL in Hamburg. Meanwhile, the candidate will develop search strategies for new classes of ‘photo-ferroic’ materials, based on symmetry and time-dependent density functional theory calculations. He/she will develop the materials specifications in collaborations with crystal growers in Oxford and elsewhere, and will be involved hands on in all aspects of the design and realisation of the experiments and the data analysis.

The experimental part of this project will be predominantly based in Hamburg, so it is essential for the candidate to be willing and able to be based in Germany for extended periods during the DPhil.

References
[1] “Femtomagnetism: Magnetism in step with light”. Uwe Bovensiepen, Nature Physics 5, 461 - 463 (2009).
[2] See for example M. Mitrano,et al., “Possible light-induced superconductivity in K3C60 at high temperature”, Nature, 530, 461–464 (2016).
[3] “Nonlinear phononics as an ultrafast route to lattice control”, M. Först et. al., Nature Physics, 7, 854–856 (2011).
[4] “Breaking Symmetry with Light: Ultra-Fast Ferroelectricity and Magnetism from Three-Phonon Coupling”, P. G. Radaelli, Phys. Rev. B 97, 085145 (2018).
[5] Disa, A.S., Fechner, M., Nova, T.F., Tobia F. Nova, Biaolong Liu, Michael Först, Dharmalingam Prabhakaran, Paolo G. Radaelli & Andrea Cavalleri, “Polarizing an antiferromagnet by optical engineering of the crystal field”, Nat. Phys. 16, 937–941 (2020).

Paolo G Radaelli

A new generation of devices, based on integrating novel antiferromagnetic (AFM) oxides with existing CMOS architectures has immense potential for low-energy electronics. The AFM oxide acts as a robust ‘write’ layer which is immune to perturbations of magnetic fields, produces no stray-fields, can be switched at ultrafast THz speeds, and is capable of generating large magneto-transport effects[1-4]. To develop this technology, it is essential to image and control the AFM state reliably. Indeed, the difficulty in imaging the AFM state has been up to now a serious obstacle in this emerging field, and has been particularly acute for topological object with complex spin textures. Techniques such as XMLD-PEEM, which rely on images acquired with linearly polarised X-rays of different polarisations and/or energies, do provide some contrast for antiferromagnets, but single-shot images are typically rather uninformative. Recently, we develop a new ‘AFM vector mapping’ approach in which many images acquired with different X-ray polarisations, energies and sample orientation are combined to provide exquisite maps of topological textures in AFM, such as domain boundaries and vortices [5-8]. This technique was applied on the I06 PEEM to great effect, first on BiFeO3 and later on α-Fe2O3. In particular, we discovered that AFM α-Fe2O3 thin films host topological (anti)merons,[6] wherein the primary ‘whirling’ parameter is the staggered magnetization. Later, we found that these textures can be generated and destroyed by thermally cycling through a spin-reorientation ‘Morin’ transition (TM) present in this material system. By applying a large ex-situ magnetic field, these textures can be wiped out and then regenerated at will. This breakthrough was recently published in Nature[8].

Although original implemented with X-PEEM, the technique we developed is equally suitable to be deployed with other X-ray microscopy techniques. Methods working in transmission (such as STXM) have obvious geometrical advantages with respect to PEEM because contrast can be produced primarily by rotating the X-ray polarisation rather than the sample. Moreover, one can apply in situ magnetic fields and image devices in operando without the difficulties associated with large electric fields. Lensless imaging employing coherent diffraction with reconstruction techniques such as HERALDO[9,10] offers a complementary set of advantages because of the fixed field of view (ideal for image reconstructions) and the greater space available for sample environment. Both STXM and HERALDO require thin samples: very recently, we were able to grow single-crystal membranes of α-Fe2O3 using a revolutionary new technique based on epitaxial growth on top of a sacrificial layer. [11] Using these samples, we obtained excellent image reconstructions of α-Fe2O3 topological textures using both STXM (at PolLux, PSI, Switzerland and HERALDO (at SEXTANT, Soleil, France). The HERALDO experiment was particularly successful, because we were able to measure the evolution of the topological textures in situ as a function of temperature (through the Morin transition) and magnetic field.

As we demonstrated previously, [5-8] Diamond provides an ideal source of soft X-rays for XMLD-based X-ray imaging of AFM domains. However, many of the aforementioned techniques and others such as soft-X-ray ptychography, tomography and laminography have not been implemented yet at Diamond. Doing so is extremely important for the magnetism user community, and would enable a wealth of experiments to be performed both on the I06 aberration-corrected PEEM, on I08 (where we have already performed a successful STXM test) and on the future CSXID beamline (currently in the design phase). The strong support for CSXID demonstrated both the interest of the community and the need to develop appropriate methodology in advance of its commissioning.

The central aim of this joint Oxford-Diamond project is to implement XMLD-based X-ray microscopy techniques at Diamond. We will develop these techniques to image topological structures in our α-Fe2O3| overlayers platform; however, these techniques have very wide applicability and, once deployed, will be available to all Diamond users. This is a 4-year project, partly supported by the Diamond Light Source, focused on the development of new imaging techniques for antiferromagnets with potential applications in IT technology. The successful applicant will be co-supervised by Prof. Paolo G. Radaelli at Oxford and Prof. Sarnjeet Dhesi at Diamond, and will spend approximately 50% of their time at each institution.

[1] P. Wadley et al., Science 351 6273 (2016)
[2] T. Ashida et al., Appl. Phys. Lett. 106 134207 (2015)
[3] O. Bezencenet, et. al., Phys. Rev. Lett. 106, 107201 (2011)
[4] X. Zhou, et al., Phys. Rev. B 92, 060402(R) (2015)
[5] N. W. Price, et al., Phys. Rev. Lett. 117, 177601 (2016)
[6] F. Chmiel, et al., Nat. Mater. 17, 581 (2018)
[7] P. G. Radaelli, et al., PRB. 101 144420 (2020)
[8] H. Jani, et al., Nature 590, 74 (2021)
[9] M. Guizar-Sicairos et al., Opt Exp 17592 (2007)
[10] M. Guizar-Sicairos et al., Opt Lett 33 (2008)
[11] D. Lu, D. J. Baek, S. S. Hong, L. F. Kourkoutis, Y. Hikita, and H. Y. Hwang, Nat. Mater. 15, 1255 (2016).
[12] T. Eggebrecht, M. Möller, J. G. Gatzmann, et al., Phys. Rev. Lett. 118, 097203 (2017).

Harnessing topological nano-whirls to enable brain-like computing

Supervisor: Hariom Jani

There are 2 Royal Society-funded DPhil scholarships available to support this project. Students will have the opportunity to be co-supervised by Prof. Paolo G. Radaelli.

Motivation: Today's computing ecosystem uses 10% of global electricity and contributes 2% of emissions (at par with aviation!). With the rise of AI, autonomous devices and big data, this energy demand will increase sharply, putting strain on global resources. The heart of the problem is that charge-based silicon platforms are volatile, inefficient and serial. This has resulted in a quest for novel quantum materials hosting rich emergent physical properties that can be harnessed to yield high-speed and energy-efficient functionalities. 

Topologically-rich antiferromagnets (AFMs), consisting of vortex-like whirling spin textures, are especially promising in this regard, as they host a robust non-volatile magnetic order. It has been theoretically predicted that such nano-whirls can move at incredible speeds of kilometres/second and host rich dynamics up to terahertz frequencies, i.e. 100-1000 times faster than conventional silicon devices. Such magnetic ‘nano-whirls’ could be used to power reservoir computing or logic-in-memory, enabling next-gen AI hardware [1]. 

We have pioneered the discovery and control of AFM solitons at room temperature, thus, experimentally opening the field of topological antiferromagnetism [2,3,4,5,6]. Our most recent breakthroughs have been published in Nature (2021), Nature Materials (2018), Nature Materials (2024a), Nature Materials (2024b), and Nature Communications (2021) etc. 

Project Scope: The goal of these DPhil projects is to push this young field toward the ultra-fast dynamical frontiers and thus open doors to its practical utilisation. Students will learn to use cutting-edge spectro-microscopy and dynamical imaging techniques to explore fast AFM dynamics. They will pioneer a versatile toolbox – involving quantum materials design, spintronic control, combined with electrical and optical excitation – to enable targeted spatio-temporal control of AFM nano-whirls. These fundamental breakthroughs are urgently needed to enable transformative next-generation applications, like terahertz nano-oscillators, AFM magnon nano-emitters and terahertz reservoir computing to develop next-gen AI. 

We are looking for passionate physics students with: 

• a strong academic track record and good exposure to hands-on research
• experience in coding or simulations (e.g. using Python, MATLAB etc.)
• a keen interest in both experimental research and computational modelling

Scientific Techniques: Successful candidates will develop research expertise in both fundamental and applied research. Depending on the candidate's interests, the project may involve the development of one or more of the following techniques in combination with computational modelling. 

Quantum materials design: Growth of high-quality crystalline thin films and free-standing nano-membranes [2-5] using integrated pulsed laser deposition and UHV sputtering at advanced growth suites in Oxford Physics, as well as at the Albert Fert Laboratory - CNRS/Thales (Paris) and National University of Singapore (Singapore).

Device fab and characterisation: Nanofabrication of prototype devices will be done using e-beam/optical lithography, laser writing and focused ion beam milling in Oxford’s Class 100 and 1000 cleanrooms. Structure/surface characterisation will be done using in-house high-resolution diffraction, reflectometry and scanning probe microscopy. Physical properties measurement system and custom-built equipment will be used to study electrical properties. 

Advanced Microscopy: Imaging of nanoscale multi-functional domains, which form the fundamental unit of information storage in oxides, will be done using X-ray spectro-microscopy techniques including X-PEEM [2,6], STXM [3], holography [7] and ptychography at leading synchrotrons - Diamond (UK), PSI (Switzerland), Soleil (France) etc. We also employ quantum NV-magnetometry, in collaboration with the Mete Atature group (Cambridge), to perform stray field imaging [4].  

Ultra-fast Dynamical Imaging: Time-resolved nanoscale dynamics will be captured using cutting-edge pump-probe X-ray imaging at synchrotrons – BESSY (Germany), PETRA (Germany) and Free Electron Lasers – FERMI (Italy), SwissFEL (Switzerland). Frequency-resolved dynamics will be captured with pump-probe micro-focus Brillouin Light Scattering. 

Simulations and Theory: Dynamical evolution of magnetic states will be modelled using Oxford’s high-performance computing service (ARC). We use both atomistic and micromagnetic software [8]. Students will also collaborate with the leading theory expert Olena Gomonay (Mainz) to develop analytical solutions. 

Students will have opportunities for extended stays in world-leading groups of our collaborators - Manuel Bibes (France), Dirk Grundler (Switzerland) and Ariando (Singapore). 

If you want to join our team, contact Hariom Jani (hariom.jani@physics.ox.ac.uk) with your CV and a statement of interest.

References:
 

[1] J Grollier et al. Nat. Electron. 3, 360 (2020).

[2] H Jani, J-C Lin et al. Nature 590, 74 (2021).

[3] H Jani,* J Harrison* et al. Nat. Mater.23, 619 (2024). 

[4] A Tan,* H Jani,* et al. Nat. Mater. 23, 205 (2024).

[5] H Jani, J Linghu et al. Nat. Commun. 12, 1668 (2021).

[6] F Chmiel, N Waterfield et al. Nat. Mater. 17, 581 (2018).

[7] J Harrison, H Jani et al. Opt. Express32, 5885 (2024).

[8] J Harrison, H Jani et al. PRB 105, 224424 (2022).

[9] ZS Lim,* H Jani* et al. MRS Bulletin46, 1053 (2021).

Dr Mustafa Bakr (PI) & Dr Peter Leek (Co-supervisor)

Over the last two decades, superconducting circuits have developed to become one of the leading technologies for quantum computing, where devices at 10s of qubits scale and quantum logic gates with low errors have been demonstrated [1]. The community is now transitioning to focus on the challenges for building a viable quantum computer at scale. Specifically, for superconducting circuits, microwave engineering expertise can dramatically help in the next stage of development, particularly, for addressing improved performance, and efficient use of microwave infrastructure for superconducting quantum computers [2]. The aim of this project to develop engineering solutions inspired by microwave filtering techniques for reliable quantum circuits at scale – based on our high-coherence superconducting quantum processor in Oxford [3]. This may include the utilisation of innovative microwave engineering design for improving coherence and relaxation times and gate speed in multiqubit circuits as well as developing frequency multiplexing methods to enable control and readout of large qubit arrays.  

The project will involve both experimental and theoretical work, including: 

• Developing and applying new theoretical tools to suppress unwanted interactions in many-qubit couplings 
• Developing engineering solution of 3D multiplexing of readout and control of quantum processers 
• Building superconducting devices using these developed techniques for high-fidelity many-qubit circuits 
• Device measurement and data analysis 

[1] Kjaergaard, M. et al. Superconducting qubits: Current state of play. Annual Review of CMP 11, 369-395 (2020).  

[2] Krinner, S. et al. Engineering cryogenic setups for 100-qubit scale superconducting circuit systems. EPJ Quantum Technology 6, 2 (2019). 

[3] arXiv.2107.11140v1 "

For more information about the project please contact mustafa.bakr@physics.ox.ac.uk. 
For more information about how to apply please contact cmpgradadmin@physics.ox.ac.uk

Dr. Safeer Chenattukuzhiyil 

Two DPhil studentship funded by the Royal Society are available for the academic year starting October 2025.

These studentships are funded by the Royal Society University Research fellowship awarded to Dr. Safeer for the project ‘Next-generation spin computing devices’. For more details, visit the research group’s website.

The DPhil projects aim to study and develop two-dimensional (2D) van der Waals (vdW) materials and their heterostructures as building blocks for advanced spintronics memory and logic device architectures.

Spintronics is an emerging research field that manipulates both electron charge and spin, offering a promising alternative to conventional electronics [1]. Early advancements in this field include applications such as hard disk read heads and magnetic RAM. The new generation of devices seeks to utilize pure spin currents (spin flow without net charge flow), typically produced in materials with strong spin-orbit coupling (SOC). By optimizing the generation of pure spin currents through the spin Hall or Rashba-Edelstein effect in SOC materials, and transferring them to a ferromagnet to induce spin-orbit torque (SOT)-driven magnetization dynamics, spintronics memory and logic devices have been demonstrated [2]. However, significant challenges to their practical implementation persist, including high power consumption and CMOS incompatibility. Therefore, new building block materials with suitable properties, such as vdW materials, are needed to develop next generation of these computing devices.

vdW materials consist of single or few atomic layers held together by weak molecular forces. Their 2D nature gives rise to unique physical properties. Notably, different vdW materials can be stacked vertically without elemental intermixing, enabling the creation of multifunctional heterostructures with atomically smooth interfaces. Recent studies showing large spin-charge interconversion effects in vdW materials and heterostructures [3,4] are promising for building spintronics memory and logic devices. For this, new device architectures made of SOC vdW materials, such as transition metal dichalcogenides (TMDC) and recently discovered 2D ferromagnetic (2DFM) materials (see figure below), will be required. Developing these is the goal of this project.

These DPhil projects are primarily experimental, involving the fabrication of van der Waals heterostructures and their nanodevices, physical characterization, magnetotransport and magneto-optical measurements to understand magnetic memory and logic device operations.

The project will be in close collaboration with Thin Film Quantum Materials (https://www.physics.ox.ac.uk/research/group/thin-film-quantum-materials) group.

For further details, email to safeer.chenattukuzhiyil@physics.ox.ac.uk

References

1. Fert, A. Nobel Lecture: Origin, Development, and Future of Spintronics, Angewandte Chemie 47, 5956-5967 (2008).
2. Safeer, C. K. et al. Spin-orbit torque magnetization switching controlled by geometry. Nature Nanotechnology 11, 143–146 (2016).
3. Safeer, C. K. et al. Room-Temperature Spin Hall Effect in Graphene/MoS 2 van der Waals Heterostructures. Nano Letters 19, 1074–1082 (2019).
4. Safeer, C. K. et al. Large Multidirectional Spin-to-Charge Conversion in Low-Symmetry Semimetal MoTe2 at Room Temperature. Nano Letters19, 8758–8766 (2019).

Amalia Coldea

ron-chalcogenide superconductors are versatile materials composed of conducting two-dimensional iron planes separated by van der Waals layers of chalcogens. When FeSe is grown as a monolayer on a suitable substrate, it exhibits the highest critical transition temperature among two-dimensional systems, exceeding that of liquid nitrogen [1]. Furthermore, ionic-liquid gating of FeSe films induces electron doping, enhancing superconductivity four-fold to around 45 K [2]. Thin flakes of FeSe also demonstrate a superconducting diode effect, where zero-resistance states appear non-reciprocally during current injection [3].

This project aims to explore the superconducting and electronic behaviour of dimensional devices based on thin flakes of highly crystalline iron chalcogenides (FeSe_1-xS_x and FeSe_1-xTe_x). Different ionic substrates and electrochemical gating will be used to tune carrier concentrations and enhance superconductivity. These studies will help establish the link between superconducting phases, electron doping, and competing nematic and magnetic phases, as well as identify signatures of topological behaviour and the superconducting diode effect. The student will investigate phase diagrams and normal electronic manifestations in novel superconducting thin flake devices, tuned via flake thickness and electrochemical gating. The project will involve device preparation, critical current measurements, magnetotransport, and Hall effect studies to explore electronic properties and superconducting phase diagrams under high magnetic fields and low temperatures. Experiments will search for quantum oscillations in the best candidate systems with large mean free paths, utilizing high magnetic field facilities in Europe and the USA. The thin flakes will be exfoliated from existing single crystals using previously developed methods [4,5]. Sample preparation will include designing appropriate lithographic patterns via optical and e-beam lithography, mechanical exfoliation, and using a glove box to handle air-sensitive samples. This project could also be extended to include simulations of current distributions in devices using finite element analysis, to better quantify and understand current distribution.

This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics.

For further reading please consult: 

1. Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3

https://doi.org/10.1038/nmat4153

2. Interplay between superconductivity and the strange-metal state in FeSe

https://doi.org/10.1038/s41567-022-01894-4

3. Field-free superconducting diode effect in layered superconductor FeSe

https://arxiv.org/abs/2409.01715

4. Suppression of superconductivity and enhanced critical field anisotropy in ultra-thin flakes of FeSe

https://www.nature.com/articles/s41535-020-0227-3

5. Unconventional localization of electrons inside of a nematic electronic phase, 

https://www.pnas.org/doi/10.1073/pnas.2200405119

Amalia Coldea

Uniaxial pressure is a powerful tuning parameter of correlated electronic phases of matter and relevant in superconducting applications. This technique can enhance superconductivity, it provides a unique insight into the behaviour of nematic electronic states giving access to the anisotropic Fermi surfaces, via the nematic susceptibility, and it can break the translational symmetry to stabilize novel topological phases of matter [1,2]. This project will use applied strain to tune the superconducting and the electronic structure. This will help develop a strategy about how to enhance superconductivity, and identify whether the pairing interaction is related to the nematic or magnetic fluctuations [3]. Additionally, elastocaloric effect can be used to probe second-order phase transitions to study the nature of complex pairing symmetries in iron-based superconductors [4]. 

Firstly, the student will perform transport and magnetotransport measurements under strain in high magnetic fields and it will establish how the superconducting phase diagrams are affected by applied strain. These studies will be extended in magnetic fields up to 90T to assess the changes in the Fermi surface under applied strain. Additionally, the student will develop capabilities to measure elastocaloric effect to determine the changes in temperature to an oscillating uniaxial stress at the superconducting phase transitions.  The strain will be applied using both piezostacks and Razorbill cells to tune electronic nematic phases and to assess the strain dependence of critical temperature. The student will use finite element analysis software to simulate the expected strain transmission for the different experimental strain design and cells. The student will be able to perform first-principle calculations to simulate the changes in the electronic structure under strain. 

Experiments in high magnetic fields will be performed at international high-magnetic field facilities in Europe and USA. As applied strain is relevant for technological applications, during the project the student could also test the strain variation of the critical currents of wires and tapes used in superconducting applications. 

This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics.

 For further reading please consult: 

 1. Emergence of the nematic electronic state in FeSe

https://doi.org/10.1103/PhysRevB.91.155106

2. Strain tuning of nematicity and superconductivity in single crystals of FeSe

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.205139

3. Iron pnictides and chalcogenides: a new paradigm for superconductivity

https://www.nature.com/articles/s41586-021-04073-2

https://arxiv.org/abs/2201.02095

4. AC elastocaloric effect as a probe for thermodynamic signatures of continuous phase transitions https://doi.org/10.1063/1.5099924

Amalia Coldea

In order to understand the relevance of novel superconductors for practical application one needs to understand in detail the three-dimensional phase diagram of superconductors using temperatures, magnetic field and critical fields. These phase diagrams can be constructed using a variety of experimental techniques which include resistivity measurements to test the zero-resistance state and the critical currents, torque measurements which probe the irreversibility fields and tunnel diode oscillator studies which can access the penetration depth. Magnetization measurements can be used to detect the upper and lower critical fields, the pinning forces as well as to estimate the critical currents using the Bean model and correcting for the demagnetizing effects.

This project will construct in detail the superconducting phase diagrams of novel crystalline superconducting materials, which would include iron-based superconductors and candidate topological superconductors. Experiments will be performed as a function of temperature and magnetic fields both in Oxford using high-magnetic fields up to 21T and at the high-magnetic field facilities in Europe and USA. The upper critical fields will be modelled using both single band and multi-band models as applied to other iron-based superconductors. The superconducting fluctuations will be explored using torque magnetometry and paraconductivity studies.

This project can be extended to explore superconducting wires and tapes relevant for practical applications using a designed probes for critical current studies up to 500 A in 14T at 4.2K. 

This project is proposed as part of the Superconductivity CDT and it will be performed in the Oxford Centre for Applied Superconductivity (CfAS) in the Department of Physics. This project will be co-supervised by Professor Amalia Coldea and Professor Stephen J. Blundell. 

For further reading please consult relevant papers:

1. Ultra-high critical current densities, the vortex phase diagram and the effect of granularity of the stoichiometric high-Tc superconductor, CaKFe4As4
https://arxiv.org/abs/1808.06072

2. Competing pairing interactions responsible for the large upper critical field in a stoichiometric iron-based superconductor, CaKFe4As4
https://arxiv.org/abs/2003.02888

3. Multi-band description of the upper critical field of bulk FeSe
https://arxiv.org/abs/2311.04188

Amalia Coldea

Discovering superconducting systems with high transition temperatures and high magnetic fields will enable future technologies. This project aims to develop novel superconducting compounds using a building-block approach, focusing on transition metal chalcogenides (such as FeSe and NbSe2) [1,2] to enhance their critical temperatures closer to nitrogen temperature. Initially, the student will prepare a series of single crystals of FeSe and its derivatives (with metal hydroxide layers separating the FeSe layers [1]) using chemical vapor transport, solvothermal synthesis, and solid-state techniques. These crystals will be modified through chemical and electrochemical intercalation of different species between the FeSe layers to tune their structures and electron doping [2,3]. This approach will also be extended to other systems, such as the misfit phases containing NbSe2 [4]. The student will employ a range of experimental tools to characterize the structure and composition of the crystals, including X-ray powder and single-crystal diffraction, neutron diffraction, and electron microscopy. Transport and magnetization measurements will be used to determine the basic superconducting properties, with potential expansion towards high magnetic field studies for the most promising candidates.

The student will use chemical-vapour growth, solvothermal synthesis in autoclaves and intercalation chemistry using reactive solutions. Other facilities include glove boxes, facilities for sealing silica ampoules, furnaces with temperature gradients. Characterisation will use the 16T PPMS in Oxford Physics and the 7T MPMS in Oxford Chemistry,  in-house X-ray diffraction and large-scale facilities on Harwell campus.

This project is proposed as part of the Superconductivity CDT. This project will be performed both in Oxford Physics (supervisor Professor Amalia Coldea) and Oxford Chemistry (supervisor Professor Simon Clarke) at the University of Oxford. 

For further reading please consult:

[1] Soft Chemical Control of Superconductivity in Lithium Iron Selenide Hydroxides Li1–xFex(OH)Fe1–ySe, https://pubs.acs.org/doi/10.1021/ic5028702.

[2] Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer, https://www.nature.com/articles/nmat3464;

[3] Intercalation in two-dimensional transition metal chalcogenides, https://doi.org/10.1039/C5QI00242G

[4] Misfit phase (BiSe)1.10NbSe2 as the origin of superconductivity in niobium-doped bismuth selenide https://www.nature.com/articles/s43246-020-00085-z

Amalia Coldea

Iron-based superconductors are a class of unconventional superconductors with high critical temperatures above liquid nitrogen temperature, and upper critical fields approaching 100T. Their parent compounds are multi-band compensated semimetals, featuring equal numbers of electron-like and hole-like carriers. The Fermi surface consists of cylindrical electron and hole pockets with significant out-of-plane dispersion. Unconventional superconductivity arises from multiple atomic orbitals with strong electronic correlations, leading to a diverse range of gap structures [1]. Despite extensive research, the pairing mechanism remains unclear due to sensitivities of the band structure to small alterations and competing magnetic and nematic fluctuations. Moreover, these systems exhibit an unusual metallic state driven by Hund’s interaction and may harbour topological superconductivity [1].

This computational project aims to use band structure calculations to simulate changes in the electronic structure due to chemical modifications and applied pressure in iron-chalcogenide superconductors. Using experimental data from angle-resolved photoemission spectroscopy (ARPES) and quantum oscillations, the project will determine tight-binding parameters to accurately describe the electronic structure of FeSe1-xSx [3,4]. Additionally, the intensity of ARPES spectra will be simulated, considering matrix element effects and orbital content, to identify anomalies induced by electronic correlations [5]. This tight-binding parameterization is essential for calculating superconducting gaps and simulating the behaviour of upper critical fields and other superconducting properties. The student will employ first-principle calculations using Wien2k and Wannier90, utilizing the supercomputing facilities at Oxford.

The project also seeks to develop guiding principles for creating an experimental database for iron-based superconductors using machine learning approaches. The student will gain familiarity with Python tools and libraries to extract information on superconducting parameters and phase diagrams from existing literature [5]. Reliable experimental data will allow machine learning tools to identify common features in iron-based superconductors.

This project is proposed as part of the Superconductivity CDT.

Useful reading:

1. Iron pnictides and chalcogenides: a new paradigm for superconductivity

https://www.nature.com/articles/s41586-021-04073-2

2. Tight-binding models for the iron-based superconductors https://journals.aps.org/prb/abstract/10.1103/PhysRevB.80.104503;

3. Wien2k,  http://susi.theochem.tuwien.ac.at/, Wannier90, https://wannier.org/

 4. Computational Framework chinook for Simulation of Angle-Resolved Photoelectron Spectroscopy, https://chinookpy.readthedocs.io/en/latest/

 5. 3DSC - a dataset of superconductors including crystal structures

https://www.nature.com/articles/s41597-023-02721-y

Dr. Safeer Chenattukuzhiyil and Prof. Thorsten Hesjedal 

This project is in close collaboration between the MIND group and  Thin Film Quantum Materials group. 

In this project, our objective is to develop novel artificial intelligence (AI) devices consisting of physical elements that replicate brain-inspired computation [1].

Current AI devices rely on executing complex deep neural network algorithms using GPUs or supercomputing facilities. However, this approach presents significant challenges, including substantial power consumption, slow operation, and privacy concerns related to online processing [2]. As a result, AI devices are not yet widely accessible for personal use. To address these issues, AI-specialized hardware chips, such as IBM's TrueNorth and Intel's Loihi chips [3], have been developed. Despite this, first-generation AI chips face scalability issues, particularly in fabricating millions of neurons and billions of synaptic interconnections. Therefore, simplified AI hardware, utilizing physical interactions to imitate neuromorphic computation [4] and capable of performing pattern recognition tasks, is expected to attract significant interest in the future, particularly for the development of offline personal AI devices.

Building on our recent work, we aim to develop groundbreaking AI hardware based on the concept that nonlinear wave interactions can physically replicate brain-inspired computing. To demonstrate this practically, we will design solid-state devices utilizing nonlinear wave interactions, such as surface acoustic waves or spin waves. We will then apply this hardware to pattern recognition tasks, including voice recognition and robotic vehicle guidance.

For further details, email to safeer.chenattukuzhiyil@physics.ox.ac.uk or Thorsten.Hesjedal@physics.ox.ac.uk

 References

[1] Lake, B. M., Ullman, T. D., Tenenbaum, J. B. & Gershman, S. J. Building machines that learn and think like people. Behavioral and Brain Sciences 40, 1–72 (2017).

[2] Mehonic, A. & Kenyon, A. J. Brain-inspired computing needs a master plan. Nature 604, 255–260 (2022).

[3] Davies, M. et al. Loihi: A Neuromorphic Manycore Processor with On-Chip Learning. IEEE Micro 38, 82–99 (2018).

[4] Marković, D., Mizrahi, A., Querlioz, D. & Grollier, J. Physics for neuromorphic computing. Nature Reviews Physics 2, 499–510 (2020).