School of Physics and Astronomy

Topological feature could prove useful for dissipationless spintronics.

Researchers in the UK, South Korea and US recently discovered that the two-dimensional layered magnet chromium triiodide (CrI₃) acts as a topological magnon insulator in the absence of an external magnetic field. This result sparked a flurry of interest in this material and its potential applications for so-called dissipationless spintronics in which electrons are used to transmit and store information in an ultra-fast and ultra-low power fashion. Thanks to detailed neutron scattering measurements and fine analysis, the team has found that this phenomenon comes from the way in which the layers in the material are stacked together. That is, while a single layer of CrI₃ is ferromagnetic, two stacked layers are antiferromagnetic which counterintuitively is different from that in ferromagnetic bulk.

Two-dimensional (2D) materials are made up of atomically thin layers stacked on top of each other. These layers are held together by weak van der Waals forces and the electrons in these materials behave very differently to those in bulk materials. For example, the “Dirac” electrons in graphene, which is one of the most famous of all 2D materials, can move at almost relativistic speeds and behave as if they are massless.

Some 2D materials are also topological insulators – materials in which electrons flow freely along the edges of a 2D sheet, but cannot flow along the surface. This effect is related to the spin of the electrons, making these materials promising for spintronic devices, which store and process information using the electrons’ spin states.

Magnons for spintronics

Certain 2D magnetic materials are also predicted to be magnetic and topological insulators. In such materials, which are very rare, quasiparticles known as magnons would travel along the edges of a sheet, much like electrons in a conventional 2D topological insulator. Magnons are collective oscillations of the spin magnetic moments of a material and are expected to be massless too, meaning that they could travel over long distances without dissipating. This property would make them interesting for spintronics applications too.

Three years ago, Lebing Chen from Rice University and coworkers found such Dirac magnons in CrI₃, which has a honeycomb lattice structure much like graphene. They came to their conclusion by studying the material using inelastic neutron scattering at the Spallation Neutron Source at Oak Ridge National Laboratory. In this technique, neutrons, which have magnetic moments, create magnons when they scatter from a CrI₃ sheet. By measuring the energy lost by the neutrons during the scattering process, Chen and colleagues were able to calculate the properties of these magnons. They found that these magnons exhibit properties consistent with them being topological and having a dissipation-less edge mode.

Spin-orbit coupling

In their new work, they performed further neutron-scattering measurements at a much larger precision as well as resolution and have found that the magnons’s topological properties arise thanks to spin-orbit coupling – a relativistic interaction of an electron’s spin with its motion. This coupling induces asymmetric interactions between spin of electrons in the materials, explains Elton Santos of the School's Higgs Centre for Theoretical Physics, Jae-Ho Chung of Korea University’s Department of Physics and Pengcheng Dai of Rice University who led the new study. These interactions make the spin “feel” the magnetic field differently, affecting their topological excitations.

Elton commented:

Surprisingly the spins have some chirality like in a mirror where left and right can work differently. We observed that without such chiral interactions, or in more complicated terms Dzyaloshinskii-Moriya exchange, we can’t describe the data.

The result has an accompanying magnetic phenomenon: a stacking-dependent magnetic order in which a single layer of CrI₃ is ferromagnetic but two stacked layers are antiferromagnetic. “The reason for this behaviour is that the interaction between stacked layers in CrI₃ is a combination of ferromagnetic and antiferromagnetic exchanges - despite apparent ferromagnetic stacking,” explains team member Jae-Ho.

“Our new work also confirms the previously observed topological nature of the spin excitation based on the Dzyaloshinkii-Moriya exchange, and rules out the competing interpretation based on the Kitaev exchange,” comments Pengcheng Dai to Physics World. “The latter is known to be an important spin-spin interaction in more complex materials (i.e. spin liquids), but not for CrI₃. This comes as a surprise to us.”

Researchers will be involved in observing the collision in the first mission to demonstrate technology to deflect an asteroid.

Mission 

NASA’s Double Asteroid Redirection Test, or DART, is the first mission to demonstrate technology to deflect an asteroid. 

DART will use an autonomous guidance system to aim itself at Dimorphos, a carefully chosen non-threatening asteroid. Dimoprhos is actually a small moon orbiting a larger asteroid called Didymos, and the force of the collision will slightly change the orbit of Dimorphos around Didymos. Because it’s not on a path to collide with Earth, the Didymos system poses no actual impact threat to our planet, yet its relatively close proximity provides an easy way for planetary defence experts to observe and measure the effect of the impact. It is expected that the collision will change the orbital period (which is about 12 hours) by a few minutes.   

The DART spacecraft will launch on a Space-X rocket in late November, and then take slightly less than a year to reach Didymos and Dimorphos, which it will hit in late September or early October 2022.  

Why planetary defence? 

Astronomers estimate that there are approximately 25,000 near-Earth asteroids close to 140 meters or larger in size – big enough to cause regional devastation if they were to hit Earth.  There is therefore a need to track near-Earth asteroids, and better understand what would be required if an asteroid was heading our way and we want to move it away from the Earth.  

Observation  

Telescopes around the world will be trained on the Didymos system before and after the collision to measure the effects and learn more about the asteroid, its composition, and the effectiveness of the deflection experiment. School of Physics and Astronomy researchers Dr Colin Snodgrass and Dr Cyrielle Opitom are part of the observing team who will study the asteroid from Earth, applying their experience of observing comets and asteroids with some of the world’s best telescopes, including the European Southern Observatory’s ‘Very Large Telescope’. 

Post-impact survey 

After the impact experiment, a related European Space Agency (ESA) mission, Hera, will launch to the same asteroid to study the effects of the collision in detail. Hera will launch in 2024 and arrive in 2026, and will go into orbit around the asteroid, to perform a forensic ‘crash scene investigation’. Combined with the observations from DART and from telescopes on the ground, Hera will give a very detailed picture of the physics of the collision process, which will allow scientists and engineers to design the most effective asteroid deflection mission, if we ever have to do this ‘for real’ on an asteroid that threatens the Earth. 

Professor Sinead Farrington who was honoured as Physical Sciences and Engineering Laureate (first place) in the 2021 Blavatnik Awards for Young Scientists in the United Kingdom awards ceremony on 25th October in London.

The Blavatnik Awards are administered by the New York Academy of Sciences, of which Prof. Farrington is now a life-member. These awards are the largest unrestricted UK science prize, with an award of $100,000 for each laureate, and $30,000 for each of two additional finalists in the three categories: physical sciences and engineering, chemistry and life sciences. 

Professor Farrington was presented the Physical Sciences and Engineering Laureate’s medal at a banquet hosted by Sir Leonard Blavatnik and the Blavatnik Family Foundation, attended by prominent scientists and policy-makers at which she gave a talk on her research, at Banqueting Hall in Whitehall, London. An open public symposium was held the following day where Professor Farrington and her fellow laureates and finalists spoke on their subjects. Professor Farrington and the Life Sciences Laureate, also from Edinburgh - Professor Steven Brusatte from Geosciences - took part in a discussion panel with BBC Science correspondent, Victoria Gill.

Professor Farrington is based in the School’s Particle Physics Experiment research group where she holds an European Research Council (ERC) consolidator grant funding her team of postdocs and PhD students searching for Beyond Standard Model particles.  She leads the UK collaboration on the ATLAS experiment at the Large Hadron Collider at CERN. She received the Blavatnik Award in recognition of her leadership of an international working group at CERN that has improved our understanding of the properties of the Higgs boson, and the development of key trigger and analysis techniques for the exploitation of Large Hadron Collider data and searches for new physics beyond the Standard Model.

Prof Farrington commented:

High energy physics is a collaborative endeavour involving very talented individuals from around the world, working together to build machines on a grand scale, and to analyse the data they generate to help us understand how the universe works at its deepest levels. I am privileged to have been able to contribute to this endeavour and to help provide some pieces of nature’s great puzzle, and am honoured to have received this Blavatnik Award.

Start-up business Dyneval Ltd, which was founded by soft matter physicists, has secured funding to establish a quality control standard that will benefit the livestock production chain.

Funding  

Dyneval is delighted to announce that it has secured total funding of over £1.8M to establish a new quality control standard for semen analysis that will benefit users across the livestock production chain.   

As part of the funding round, Dyneval secured a £575K grant from InnovateUK under the Transforming Food Production Series A Investor Partnership. Securing lead investor support from Jim Dobson of Cottagequinn Enterprises Ltd within the Series A Partnership, and through a collaborative funding investment round led by Kelvin Capital and supported by Par Equity, Gabriel Investments and Scottish Enterprise, a further £1.293m of equity investment was raised.    

Entrepreneurial effort  

Dyneval was established by Dr Tiffany Wood and Dr Vincent Martinez in April 2020 to offer innovative technology for the precise measurement of semen quality in order to improve the profitability and sustainability of farming. Tiffany and Vincent have a background in the physics of complex fluids, which can be described as ‘liquids with bits in them’. 

The challenge 

Over the past 40 years, conception rates in cattle have fallen by 20% and this is costing the average UK dairy farmer over £37k each year.  To assess semen quality on farm, vets rely on visual assessment using an optical microscope and data has shown that veterinary assessment can vary by as much as 40% so that vets err on the side of caution when advising farmers. The Dynescan, from Dyneval, is a portable instrument that provides reliable measurements of semen quality on the farm so that damaged or inferior quality semen can be discarded to ensure that only top quality semen is used for reproduction. This will save many cows from returning for insemination, improving their welfare while improving the operational efficiency of farms. Predictions indicate that if conception rates can be elevated by 27%, the carbon footprint of farming could be reduced by up to 20% [Garnsworthy, Animal Feed Science and Technology, 112, 2004]. Improving the sustainability of farming is a win-win-win: it helps farmers, improves animal welfare and is better for the environment.    

Future plans

Next month, Dyneval will move address to the Roslin Innovation Centre based at the University of Edinburgh’s Easter Bush Campus and within a cluster of the highest concentration of animal related science expertise in Europe.   

New results from the MicroBooNE experiment deal a blow to a theoretical particle known as the sterile neutrino.

No sign of the sterile neutrino 

For more than two decades, this proposed fourth neutrino has remained a promising explanation for anomalies seen in earlier physics experiments. Finding a new particle would be a major discovery and a radical shift in our understanding of the universe. 

However, four complementary analyses released by the international MicroBooNE collaboration all show the same thing: no sign of the sterile neutrino. Instead, the results align with the Standard Model of Particle Physics, scientists’ best theory of how the universe works. The data is consistent with what the Standard Model predicts: three kinds of neutrinos - no more, no less. 

Neutrino detector 

MicroBooNE is a 170-ton neutrino detector at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, which is roughly the size of a school bus and has operated since 2015. The international experiment has close to 200 collaborators from 36 institutions in five countries, including the School’s Dr Andrzej Szelc, who is the MicroBooNE UK Principal Investigator (PI). They used cutting-edge technology to record spectacularly precise 3D images of neutrino events and examine particle interactions in detail—a much-needed probe into the subatomic world.  

What are neutrinos? 

Neutrinos are one of the fundamental particles in nature. They’re neutral, incredibly tiny, and the most abundant particle with mass in our universe—though they rarely interact with other matter. They’re also particularly intriguing to physicists, with a number of unanswered questions surrounding them. These puzzles include why their masses are so vanishingly small and whether they are responsible for matter's dominance over antimatter in our universe. This makes neutrinos a unique window into exploring how the universe works at the smallest scales. 

First hints of sterile neutrinos 

Neutrinos come in three known types—the electron, muon and tau neutrino—and can switch between these flavors in a particular way as they travel. This phenomenon is called “neutrino oscillation.” Scientists can use their knowledge of oscillations to predict how many neutrinos of any kind they expect to see when measuring them at various distances from their source.  

Neutrinos are produced by many sources, including the sun, the atmosphere, nuclear reactors and particle accelerators. Starting around two decades ago, data from two particle beam experiments threw researchers for a loop as they saw more particle events than calculations predicted. These strange neutrino beam results were followed by reports of missing electron neutrinos from radioactive sources and reactor neutrino experiments.   

Sterile neutrinos emerged as a popular candidate to explain these odd results. While neutrinos are already tricky to detect, the proposed sterile neutrino would be even more elusive, responding only to the force of gravity. But because neutrinos flit between the different types, a sterile neutrino could impact the way neutrinos oscillate, leaving its signature in the data. 

Next steps in neutrino research 

MicroBooNE’s new results are an exciting turning point in neutrino research. With sterile neutrinos further disfavored as the explanation for anomalies spotted in neutrino data, scientists are investigating other possibilities. These include things as intriguing as light created by other processes during neutrino collisions or as exotic as dark matter, unexplained physics related to the Higgs boson, or other physics beyond the Standard Model. 

Quantum Mechanics is a textbook written by two members in the School of Physics & Astronomy. Published by Cambridge University Press, the book is going to be available on Thursday 21 October.

Quantum Mechanics is a textbook written by two members in the School of Physics & Astronomy, Prof. Arjun Berera and Prof. Luigi Del Debbio. 

This book presents a modern coverage of Quantum Mechanics. Beginning with a detailed introduction to quantum states and Dirac notation, the book includes - among others - a chapter on symmetries and groups, important components of current research; and a comprehensive chapter on quantum entanglement. This subject is rapidly growing not just in the field of physics but also in communication, computing and encryption. To date, however, there have been limited sources for undergraduate students to get a basic introduction to the subject. The various exercises in the text expand upon key concepts and further develop students' understanding.

I had no idea how much work would be needed to turn a bunch of lecture notes into a proper book! Without the curiosity of the students, the patience of the editor and Arjun’s support, I would have given up long ago. I am very happy to have a book that introduces Quantum Mechanics in a format that aims to be suitable for lectures. Writing a textbook, as opposed to a comprehensive treaty on Quantum Mechanics, was our main challenge (Prof. Luigi Del Debbio)

The early motivation for writing this book was that both authors were - and still are - teaching Principles of Quantum Mechanics in the School of Physics & Astronomy, a course taken by Mathematical and Theoretical Physics students (the second semester of this course is also the Quantum Physics course). The lectures from this course provided an initial baseline for the book. The project has been developing for over seven years and has expanded from the lectures of the course into what is now this textbook

At the onset of starting work on this book, I felt there was a missing element in undergraduate quantum mechanics courses: namely a comprehensive treatment of quantum entanglement that could be covered in a 2-3 week module.  I had formed a set of lectures on this subject for the second semester of the Principles of Quantum Mechanics course, which I thought were fairly successful and the input and interest from the students was helpful in making improvements. Those lectures were the basic material for the chapter on quantum entanglement in the textbook. It was a lot of work to produce this chapter, but I hope readers find it helpful. This chapter had to fit coherently with all others to produce a textbook. As Luigi and I had taught Principles of Quantum Mechanics for many years, it made it very easy to have a coordinated effort in writing this textbook, especially since we both were supportive to each other in this work (Prof. Arjun Berera).

The Astronomer Royal for Scotland, Professor Catherine Heymans, has officially opened Aberdeen Science Centre following its £6million redevelopment.

Aberdeen Science Centre reopened to the public last November after a major project to create an aspirational science centre which reflects the STEM priorities for both industry and education. More than 60 new interactive exhibits over two floors now await visitors.  

Around 100 invited guests attended the official opening, where Professor Heymans unveiled a commemorative plaque to mark the centre’s transformation.  

An astrophysicist and a world-leading expert on the physics of the dark universe, Professor Heymans became the first woman to be named Astronomer Royal for Scotland earlier this year. Accepting the almost 200-year-old honorary title, she said she wants to use it to encourage people to develop passion for science and promote Scotland internationally as a world-leading centre for science. 

Professor Heymans said:

It is a great honour to join Aberdeen Science Centre in celebration of its reopening. A fantastic visitor attraction with outstanding interactive hands-on exhibits, Aberdeen Science Centre provides the perfect place for curious young minds to have fun exploring the wonderful world of science and technology.

The centre’s exhibits are aimed at all ages and are themed into six zones: Energy; Space; Life Sciences; Make It, Test It; and a dedicated area for the under-6s, as well as the Shell Learning Zone, where science, technology, engineering and mathematics (STEM) are brought to life. New exhibits include RoboThespian, a chatty humanoid robot sponsored by the centre’s Digital Futures Partner, Equinor, and The OPITO Theatre of Energy – the UK’s first immersive experience of its kind.  

Bryan Snelling, Chief Executive of Aberdeen Science Centre, said:

We are delighted to welcome Professor Heymans and our invited special guests to mark the official opening of Aberdeen Science Centre following its fantastic redevelopment. This is a celebration of all the work that has gone into redeveloping the centre to transform it into a modern visitor attraction which showcases STEM innovations through educational and fun exhibits and events.

Dr Maxwell T. Hansen has been awarded the 2021 Kenneth G. Wilson Award for Excellence in Lattice Field Theory.

Since its inception in 2011, the annual award has recognised physicists who have made recent, outstanding contributions to lattice field theory – the study of quantum field theories on discretised spacetime (the lattice), amenable to simulation by computers.  

The award was presented at the annual Lattice International Conference. 

Max is a UKRI Future Leaders Fellow within the Institute for Particle and Nuclear Physics. His research focuses on extending the reach of numerical lattice calculations to extract more complicated observables governed by the strong force of particle physics and, more broadly, predictions of the full Standard Model. Specifically he has made significant developments in methods for extracting multi-particle scattering amplitudes, based in techniques that use the finite system size of the simulation as a useful probe of the interactions (rather than an unwanted artifact). 

The award is named after Nobel Laureate Kenneth Wilson (1936–2013), who formulated lattice gauge theory in 1974, thereby improving our theoretical knowledge of non-perturbative quantum field theories and eventually permitting such theories to be studied numerically using world class computers. 

Congratulations to colleagues who have received fellowships and awards in this latest round.

The Royal Society of Edinburgh (RSE) has announced its funding outcome with focus on creating and strengthening collaborations. 

Early Career Fellowships  

Congratulations to the following who have received RSE Saltire Early Career Fellowships:  

• Dr Benjamin Giblin, postdoctoral researcher in cosmology, will receive funding for his project on ‘Shining Light in the Dark: Enhancing Insights into the Dark Universe with Gravitational Lensing and Machine Learning’, collaborating with researchers at the Universitat de Barcelona. 
• Dr Nathan Moynihan, postdoctoral researcher based in the School’s Particle Physics Theory group will work with colleagues in the University of Dublin on ‘Scattering Amplitudes, Gravity and the Celestial Sphere’. 
• Ms Frederika Phipps, PhD student, is collaborating with the Instituto de Astrofisica de Canarias on ‘Globular Clusters in Cosmological Simulations: Evolution Beyond Formation’. 

The RSE saltire early career Fellowships provide PhD students, postdoctoral researchers, and Early Career Researchers with a 3–12 month opportunity to focus on a research project of their choice in a university or research institute in another country. The fellowship supports career development and high-quality research production through European connections and collaboration via research placements. 

Project collaboration awards

Prof Richard Blythe’s work on ‘Statistical mechanical theories of emergence in biological systems’ has received a RSE Saltire Facilitation Network Award. This is in partnership with colleagues from the Statistical Physics and Complexity Group at Edinburgh, the Institute for Theoretical Physics at the University of Göttingen and the Max Planck Institute for Dynamics and Self-Organization. The award is designed to create and consolidate a collaborative Scotland – EU partnership over a two-year period.  

Dr Sean McMahon has been awarded an RSE Saltire International Collaboration Award.  This award aims to facilitate international collaboration between researchers based in Scotland with researchers in the EU for up to two years, in this case, colleagues in the University of Uppsala. Their collaboration will focus on improving our understanding of how to recognise the earliest evidence of life in our solar system. 

Royal Society of Edinburgh  

The RSE is an educational charity providing public benefit throughout Scotland. This round of grants totals £1,805,000, funded by the Scottish Government, through the RSE Saltire Research Awards. Grants covers a total of 93 research projects across Scotland. 

Prof Aliotta receives the Giuseppe Occhialini Medal and Prize in recognition of her work in nuclear astrophysics.

Giuseppe Occhialini Medal and Prize 

The Giuseppe Occhialini Medal and Prize is awarded jointly by the Institute of Physics and the Italian Physical Society for distinguished work by a physicist based in Italy or the UK/Ireland. 

Prof Marialuisa Aliotta received this award for her major contributions to nuclear astrophysics experiments, in particular to the study of key hydrogen-burning reactions relevant to quiescent stellar evolution and nucleosynthesis, in the framework of the international LUNA experiments at the Laboratori Nazionali del Gran Sasso, INFN (Istituto Nazionale di Fisica Nucleare). 

Investigating the nuclear reactions in stars 

Her research interests focus on experimental nuclear astrophysics, specifically on the investigation of nuclear reactions that occur in stars and govern their lifetime and evolution. These reactions are also responsible for the creation of new chemical elements both in quiescent stars like our sun and in explosive scenarios like novae, supernovae, and X-ray bursts. 

Quiescent stellar evolution involves reactions mainly between stable nuclei at energies well below the Coulomb barrier of the interacting species. Their experimental investigation in a terrestrial laboratory is severely hampered by the background induced by the cosmic rays in the detection devices. Thus, a unique approach consists in carrying out measurements underground, where the background induced by cosmic rays is suppressed by orders of magnitude. Over the last ten years, Marialuisa’s research has been conducted at the world leading Laboratory for Underground Nuclear Astrophysics (LUNA) at the INFN Laboratory Nazionali del Gran Sasso (Italy). Prior to joining the LUNA Collaboration in 2010, Prof. Aliotta proposed and performed experiments at Radioactive Ion Beam facilities (TRIUMF, GANIL, CERN) mainly to study (α,p) reactions on unstable nuclei, many of which are crucial to drive explosive scenarios such as X-ray bursts. These measurements are also difficult to perform because of limitations in radioactive ion beam species and intensities. New opportunities are now opening up with the use of storage rings such as CRYRING at GSI (Germany). 

Prof Aliotta commented: 

I’m delighted to have received the Giuseppe Occhialini Medal and Prize for 2021. As it is often the case, awards to individuals are never entirely their own. So, aside from my personal recognition, the prize is also a recognition of the outstanding work of the entire LUNA Collaboration. My heartfelt gratitude goes to all my colleagues at LUNA and in particular to Dr Carlo Bruno and Prof Thomas Davinson for their extraordinary contributions over the years.